I was basically happy with beersmith during my brief use of it (this was before the last update) and for some reason I decided to give the up and coming BTP a shot sight unseen. After getting over the learning curve, it worked well for me despite a few shortcomings that are being addressed in the upcoming 1.5 release. Now that I'm much more versed in all grain technique/process than I was when first trialing beersmith, I don't have a good feel for which is better. I haven't seen a side by side comparison list of features supported/not supported for each package. One thing is for sure, BTP's interface is pretty.
One thing to consider, if all of the big three are basically the same in functionality, I'd go with BS first because it looks better than promash and has more users than BTP.