Pecan Lodge - The lines are absurd. Fitting it into his schedule may not be that easy. They open at 11:00, and the line begins a little before 10:00. If you get in line after they open, plan on a minimum of an hour and a good chance they will have ran out of something.
Lockhart - Better lines and takes food off the pit twice a day so you stand a better chance of getting what you want. Sells clod (only place out of hill country) which is my favorite cut. Is a restaurant/bar, so different vibe than Pecan Lodge. PARKING IN BISHOP ARTS DISTRICT SUCKS!
Slow Bone - Solid Texas BBQ. Close to Downtown. Easy to get to and to park.
North Main - Really good buffet style (serves a ton so it is always fresh and hand cut). Only open Fri-Sun. A little bit out of the way (between Dallas and Fort Worth). A real gem of a place IMO.
3 Stacks - Well north of the city (Frisco). Nice sit down restaurant/bar. Great Q including beef short ribs.
Hard 8 - Kind of a chain (there are 3 of them), but not really. The one in Coppell (not far from downtown) is the best. The original is in the middle of nowhere about 1.5 hours south of the city and is nowhere near as good as Coppell. Probably the one I would send someone who doesn't want to make an adventure out of the trip and wants to stay close to the city.
Hutchins - My personal favorite in DFW (and not just because it is a couple of miles from my house). Like Pecan Lodge and Lockhart, it is a Texas Monthly top 50 joint. Has AYCE (not buffet - a waitress brings you a plate of fresh sliced on demand) and normal plate pricing. Free dessert and fixins bar for all dine in customers. Nice balanced flavor profile IMO (Pecan Lodge for example is too salty/peppery and only does fatty really well - I have a hard time saying anything is too salty or fatty so...). It is a bit out of the way but an easy trip up 75. Long hours and pretty much never runs out of food until right before closing. Tons of parking. This is where I take everyone who comes to DFW.
That hotel is a bit north of downtown, so Hutchins and 3 Stacks are both more convenient than one might think (especially 3 Stacks since the hotel is right on the Tollway that leads into Frisco).
If you need anymore info, feel free to PM me.