I'd get the .45.
IMHO, having owned one for a while, I just don't like the SKS that much. Accuracy is so-so. Scope-mounting options are fairly gimmicky and limited, and most importantly, that danged thing is HEAVY. It might would help if I removed the folding bayonet (but I'm not gonna because then I'm 93% certain I'd misplace it
), but as it is it's just bad. Not just heavy either - I have some other rifles that are just plain heavy, but SKS is heavy AND poorly balanced - it is front-heavy.
Overall, though I know they cost more, I personally see the AR15 as a much MUCH better choice for a semi-auto. When the SKS was $89 (what I paid for mine) and the AR15's were $700+, then it wasn't enough better to care. Now that SKS's have shot up in price though, I just can't see buying one. If I could trade mine for a decent 1911 I would in a heartbeat.
That said, seeing that I did pay $89 for mine, and I'm leaning more and more towards selling it, I guess the recent rise in going price is a good thing
.