I went to these two during my most recent trip to DFW. Can't say I was impressed with either.
I'd rate Longoria's BBQ as the better of the two. Ribs(decent rub on the ribs) and brisket had a bit of smoke to them, but they were both a little dried out. Their sausage(made from ground brisket) had potential but needed more spice. The fries were mushy baked crinkle-cut and not to my liking at all. On the other hand, the ranch beans and the pinto beans from Longoria's were excellent.
Didn't care for Mesquite BBQ much. Ribs had very little smoke to them. Didn't realize until I got to my table that they'd given me all "inside" meat on the brisket which tasted more like pot roast than 'cue. I did like their sausage which comes from a supplier called Rudolph's according to a review of Mesquite BBQ I read. Their barbecue baked beans were okay. Fries had really absorbed a lot of grease and weren't very good.