Well I have most of the rulesets mentioned in this thread and I find myself facilitating between more than a few of them.

This is not helped by the fact that I am a solo gamer and the only drive to use a set is my own, I think that sometimes a bit of peer pressure can be a good thing?
The sets I flip-flop between in no particular order are:
W40K 3rd edition
One Page - Grimdark and Grimdark Firefight
Necromunda - 2nd ed I think
One hour skirmish and wargames rules
FFOL bigger battles and other titles
Space Station Zero
Xenos and Lion Rampant (2nd)
Stargrave
Zona Alpha and solo version
Many, many others.......ad nauseum
I also have Deathship one but have not played it yet.
The ones that lend themselves easiest to solo play are 40K 3rd because I have played them so long the rules are mostly invisible to me, if that makes sense but its very setting makes me drift back into the 40K orbit all the time as do One pages Grimdark and GD firefight (All I play with random drawn activation), when sometimes I really would like a more general scifi feel. Stargrave has to-many special rules and I don't like D20's (also see Space Station Zero), and I always end up restating to 40K and then playing the Stargrave mission with no magic ....
Xenos Rampant is fun but again lots of potential special rules and I find the activation rolls a bit of pain.
FFOL bigger battles I also like but is not so easy to adapt for solo unfortunately because of the activation cards

, one hour skirmish I also like but dealing both packs of cards is also a bit of a bummer.
In short I have tried many rules and I like bits of lots of them but not all of any one ruleset and oddly 40K 3rd keeps resurfacing as it is simple if you ignore codex creep, however no matter how hard I try it still is a bit to-40K based for me for use as general set of sci-fi wargaming rules.
All of this nonsense may not be much help to you unfortunately, and for this you have my apologies, but at least you are not alone

Glen