I'm currently running a Traveller game (about 5 sessions in) and have looked at Stars Without Number quite alot.

Stars Without Number is mostly "DnD 2e in space" with classes, levels, and THAC0 but, for some reason, tacked on a 2d6 skill system. I dont really like it, mechanically, because of that. Also, the ship combat is really crappy and comes down to a guessing game more then anything.

However, SWN does have a sick ass NPC faction and world tag system. I cannot understate how much content I have gotten out of two different campaigns just from using the SWN faction system.

Mongoose Traveller on the other hand has had 8 different versions of Traveller before it to refine the mechanics and balance things. Every skill or attack roll is 2d6 + Mod where 8 or greater is a success. Character generation breaths life into your characters before you even have a chance to control them thanks to the random nature of it. Ground combat is very much a game of managing your initiative. Initiative is dynamic depending on a weapon's recoil and how many attacks you want to dodge. Ship combat has a reasonable amount of depth and, once again, involves managing your resources.

What I ended up doing is using Traveller as the main game and pulling the faction and trade systems from SWN.

Traveller's rules for creating a robot are, for my eyes at least, hideously complex.

Which book are you getting those rules from? I have heard not so good things about the official Book 9: Robots. I ended up skipping it and picking up a third party published Robots by 13Mann. Yes, the rules take a bit of reading, but from what I'v done they make sense and are very flexible.

As far as ship building goes, it does take a bit with Traveller. It took me about 2 times reading through the section to understand it but now I can build a complete ship in like 20 min. Pick hull size, add the critical systems, use the remaining mass for mission specific things.

Creating worlds...it depends on what you want. Traveller's system gives more depth. You get details like gravity, atmosphere, hydrographics, starport type, population, tech level, law level, etc. If you dont need or want that much detail then you could easily use the SWN rules.

I have not had to generate any aliens yet, but the two times I looked over the rules leads me to believe I can have an alien in like 5 or less dice rolls.

It sounds to me you already spent the money and got the Traveller core book. So the best thing you could do is download the free SWN book which has the faction and planet generation in it.