First, Traveller allows you to span a galactic empire, if you chose, with lots of different races, planets, ships, etc.

The Frontier is a small, cutoff sector, possibly surrounded by hostile Sathar clans.

The technology, especially for starships, seems to be greatly different. And, heck, Traveller has far more canon modules and other source material to work with. Star Frontiers has a more open play setting... because much of it is undefined.

I think you need to separate setting from rules in your question.

Traveller= space opera

Star Frontiers = Western with a side of robber baron rail road tycoons in the form of mega corps.

My Scilian plumbing partner said of wine: "Drink what the hell you like" This advice applies to most things in life and same for RPGs I think.

Some people play Star Frontiers with savage worlds or Frontier Space or home brew or other. Can't say much about Traveller in that reguard although rumor has it that you might not survive character creation. LOL.

1> Personal combat is very survivable. To expand on the wild west comment made earlier in the thread --- unlike what Gollywood would like us to believe, gunfights took a long time to resolve due to low quality control in the ammunition. No two cartridges were the same, powder equality and lead uniformity were both pipe dreams back then so accuracy was an interesting game to play. In other words, both sides would reload several times each before someone finally hit the other person. Such as it is in SF, because instead of crappy ammo the damage dealt is pathetically non-lethal in many cases...so just like the old west, you'll be reloading a lot before someone kicks the bucket.

2> Subspace communication. It doesn't take a year to get information to the other side of the Frontier, instead it takes a few hours or a couple days tops, depending how far away the receiving world is. In other words, if someone rats you out as you begin to leave a system, the next system will know about it long before you get there.

3> Artificial gravity. Simply put, if your ship is moving you have gravity. If it is coasting along you're in zero-G. There are no gravitics in SF, instead the decks-perpendicular-to-main-axis design allows gravity under thrust. Anything else is a house rule.

4> Setting - unless your Traveller experience is limited to the original core three LBBs, there really isn't much definition in the Frontier. There's the UPF versus the Sathar. There's a few definitions for how UPF Spacefleet works in the campaign. There are a handful of systems and a map showing where they are in relation to each other. Aside from Volturnus (Zebulon system) being fleshed out in the original boxed set/Alpha Dawn and the three modules coinciding with those sets, you're pretty much on your own for filling in the details in the rest of the Frontier. In other words, you make it YOUR Frontier. Your Frontier won't be anything like my Frontier or Jedion's Frontier or Joe Cabada's Frontier It's the B/X D&D of SciFi in that regard.

5> Speaking of B/X D&D, it's a simple set of rules that is very flexible...much like sticking with just the three core LBBs in Traveller would be if one was so inclined. Being new to Traveller myself, I can attest to how addictive acquiring those other booklets can be...it can get rules-heavy quickly if you let it. SF didn't enjoy the publication expanse that Traveller did (and still does to this day).

6> Zebulon's Guide to the Frontier - Just ignore this. The creators ignored everything that preceded it, so you should too. You'll find a few ideas that can be incorporated in the original game but don't even try to make any sense of it from there. The creators certainly didn't try to make any sense out of it (unless nonsense counts), and honestly had the other two volumes been released I sincerely doubt it would have seen much in the way of improvement. 

This, of course, is a matter of opinion. As is this: my rpg group got a lot of mileage out of Zeb's Guide when it was first published, and ported some of it over to Alpha Dawn when we played again a few years ago. So, don't ignore it. Read and see if there's anything in it you like and feel you could use for your game.

After many years of playing and running Star Frontiers games, I don't think I or any of my players saw it in that light. Possibly because we're not Americans   SF was more approachable as an RPG than Traveller to a unch of 12 to 14 year olds in the early 1980s. I'd played Traveller but Star Frontiers just seemed less fiddly to get up and running. Also it was less lethal in terms of character generation

Yep, pretty much what I said...adapt what you like from it. 

Replacement mechanics for the original game (i.e. 2e SF)? Forget it.

Again, that's your opinion. There's nothing wrong with 'Column Shift' system. We used it for many years and even adapted it for use in some other rpgs. Similarly, we got a lot of mileage out of Zeb's Guide and only recently decided to port bits of it back to Alpha Dawn (after not playing SF for 20+ years). And we only went back to Alpha Dawn out of sheer nostalgia, not practicality. Originally we were just going to use Zeb's because it was more useful to us and we remembered more about it than AD after a gap of several decades

So, in the interest of fairness, 'just ignore this' isn't necessarily a fair overview of Zeb's Guide. You don't like it - fine. But it's unwise to tell others to ignore when not everyone thinks Zeb's is crap.

My wisdom must be showing then, as I didn't tell anyone to ignore it "because it's crap." 

What I said was "to ignore it because the creators ignored everything preceding it." Seriously, they butchered a lot of what was printed in the former rule books in many ways, starting at the beginning with Volturnus/Zebulon. The more I read it the more I found it did not mesh with the game I grew up with that preceded it. I distinctly remember picking this up back in 1985 and reading it for the first time where I checked the cover more than once to see if it was Star Frontiers.  

As the former champion of Zebulons Guide Revisited project I'm now closer to Shadow's Orbit on forget Zebs Guide.

If you want some new goodies/equipment sure raid it

If you want some ideas from the time line (without actually using the timeline) sure, raid it (clarification I would use a detail on the mechanon's gleaned from the timeline without using the timeline because of all its idiotic problems)

If you want to use the cadres and mega corp setting information, which is compiled from KHs and a Dragon magazine for the most part, sure raid it.

If you want to use the new races or the new star systems or the new planetary notes then sure, raid it.

RE: column shift mechanic

 no body now uses this, only Zebs and a superhero game did back in the day for the most part its slower than having a target number and rolling dice.

and with a character sheet and dice you really dont have to waste time looking anything up 1/2 ability score plus 10%/level is right there on the character sheet and you roll. and all subsequent combat rolls shouldn't require relooking at the character sheet as you should be able to remember that one number vs constantly comparing and consulting a column shift chart for every single dice roll. To be sure if you like the it then use it, some people reportedly played and enjoyed Rolemaster.

I'm forever sold on the fast play of AD style mechanic after having run two separate combats in 1/2 hour plus some skill checks and role play in that same half hour then played D&D 3.5 for 3 hours where we only got through 1 combat -that was tedious.

Zebs is a chinese menu- pick and choose what appeals to you. Ultimately not a fan of it. Although i do slum with it now an then but in those cases we can blame that on the synthetic alcohol.