You'll likely get a bunch of different (conflicting) responses. According to Kodak, T-Max 3200 (TMZ) is nominally an 800-1000 speed film. Ilford puts Delta at 1000-1200. So they are more or less the same real speed, with Ilford being a hair faster. Most people I've heard think Delta is a bit lower in contrast if not developed longer. I think TMZ works just fine at 800 or 1600, whereas I've been told that Delta is harder to make workable at 800. Delta is obviously available in 120 as well - if you shoot 35mm and 120, then just use the Delta. From shots of others that I've seen, I feel like Delta is a bit grainier. Of course, there will be others who say the opposite - a lot depends on your developer and exposures.
Discussions of tonality of the two films are difficult to decipher, since so much of that depends on metering, exposure, development, and printing/scanning. And when you start pushing films, and these two films are often exposed at 3200, which is a 1+ stop push, tonality usually suffers due to the underexposure of shadows and increase in contrast from extended development. So you might be better off making your own decisions here.
I use and prefer TMZ. I've used the Delta once or twice, but since TMZ is working for me in my developer of choice, XTOL, I'm sticking with it for now. It's actually one of my favorite films. I often shoot it at 1600, where it looks pretty good. When I feel like it's appropriate, I'll rate it at 800. It looks wonderful there. 3200 starts getting a bit pushed looking for me; I'll do it if I have to, but if I have enough light for 1600, I shoot it at 1600. It's a great film for traditional darkroom printing in my opinion. Lastly, while it is grainy, it has about the same resolving power (or a bit more) than Tri-X in my casual tests.
One thing I will say, since these are high speed films, most people shoot them in low contrast poor lighting. They can really shine if shot in environments with decent lighting - I think they get a bad rap because they are shot in such difficult situations.
I can share with you some shots if you'd like.