I like the 280x toxic, because 280 is a great architecture, and the toxic is the best 280x card (in my opinion).
it is a powerdrawer though if not properly undervolted!
If you have to decide between 280x toxic or 290 tri x and 290 cost just 50 dollars more, which you choose?
290... 50$ for 100 KH/s is a no brainer.
that depends on the base price! lets look at kH per Dollar
280x toxic gives me 760kH -> 760/$400=1.9, 760/$450=1.68, 760/$500=1.52
add 50 dollars
290 tri-x might give 900kH -> 900/$450=2, 900/$500=1.8, 900/$550=1.63
290 wins.
my opinions
it depends on the setup, I run many 290 cards, but the 280x is the best, so if it is a single/dual card setup, I might go for the toxic. cooler more efficient and less noisy.
the 280x toxic (might even go with the tri-x, is cheaper) is a great (maybe the best card), the 290 tri-x is almost reference with better cooling, but some people report problems...