Which torch to buy for finishing sous vide meat? Butane or propane?
I use Propane all the time.  There are several factors as to why:


It is cheap, about 1/4 the price of butane.  
It’s more readily available.  You can buy a propane torch at many different stores for very cheap.  
The torches typically put out a lot more heat.  I’ve used both propane and butane, mostly for crème brulee, but other food as well.  The butane torches put out such a focused small area of heat, that it would get uneven burning.  Whereas with Propane, they often put out a much larger area of heat, making it easier to caramelize across the surface evenly.


As for the concern of it imparting propane flavor, I have had that happen, once, but I’ve also had that happen with butane.  It’s all about flow control.  If you have the dial turned up too high and it’s spewing out massive amounts of propane, plus hold the flame too close to the food, you MIGHT get then hint of propane.  But if you have the torched dialed in to the proper settings, you really can’t beat the ease and convenience of “energy-efficient clean-burning propane gas”