All else equal, longer wheelbase is preferred. However, between the Tahoe and Suburban, all else is not equal. The distance between the ball and rear axle (rear overhang) is larger for the Suburban vs. Tahoe. The differences overall are not significant enough to limit your choices if towing behaviour is the most important aspect. Choose the one with higher payload (which in my experience has been the SWB for same equipment) or what fits in garage. If you plan to use the 3rd row seats on a regular basis, skip the Tahoe. The 3rd row space is cramped and there is no cargo space behind it when up/in use.
6200 dry is a lot for these SUVs,though. That will be 7000-7500 loaded with 900 pounds of TW, leaving 500-600 payload left for people and stuff. Seems enough to me for a couple, but maybe not a growing family of 5+.