what do i chose for my build? 2 770's or s r9 280x's?
280x for the extra vram.
2 770 if you want good performance with lower wattage.
2 280x's for pure performance. will need more power so make sure your psu is up for it.
If you want to see a direct comparison: http://www.anandtech.com/bench/product/1058?vs=1064
It really just depends on which games you want to play. Although, I'd recommend getting a 290(x) or 780 (Ti) instead, simply because single card setups are much less headache.
was there a heating issue with the 290?
There is on the reference models. With a non-reference card, it's great.