To offer a different perspective, I sold my XRT and went to Smarty. Not because I didn't like the tunes. Not because I didn't like the smoke. But because of my results on a dyno.i have run a number of programmers and just started running the XRT a few weeks ago. i LOVE it! the tunes are great. i was torn between the Smarty and XRT, and 2 things really swayed me. i feel there are too many settings to deal with on the smarty, and all of the head gasket issues weren't looking good. also i was looking in the classifieds on here and it seemed that the Smartys to XRTs for sale were like a 3 to 1 ratio. that's not good. these are only my observations and opinions, it seems there has been a bit less trouble with the XRT and certainly less parameters to deal with. some want all of those setting. i can say you would likely love the XRT tunes though. oh yeah the XRT smokes more than the others too.
It seems both tuners can perform entirely different on each truck. There's really no rhyme or reason to it. I just found one worked better for me.
As for which one, if the OP can try both, I'd suggest it.