To summarize what most people have said here:
The pros of a triple nowadays pretty much comes down to having a wide range of gears (but not necessarily a lower low gear than a compact double) with less of a jump between gears.
The pros of a double are that you don't have to lose the same lowest gear, and the shifting of the chain rings tends to be smoother with less need for tuning due to the fact that you're dealing with 2 rings instead of 3 and in addition, the distance the derailleur has to travel is less. So it's mechanically a little simpler. That and the weight issue.
My BF does custom bike builds for a living and he still has clients that want a triple over a double. And yes they are available but sometimes hard to source. So if you really want a triple, it's possible but I wouldn't give up on the compact double idea.
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2007 Look Dura Ace
2010 Custom Tonic cross with discs, SRAM
2012 Moots YBB 2 x 10 Shimano XTR
2014 Soma B-Side SS