I got into the GMT800 platform from a friend who was really into Ford superduties. He had a 7.3 diesel Excursion and convinced me it was the best SUV on a truck platform. I bought a 7.3 Excursion with 300k miles on it O_O, and it constantly had issues, most of them I had no idea how to fix since I had never worked on a Diesel (let alone the 7.3 which has a weird engine design). So after thousands of dollars into repairs and many more on the horizon I sold the Excursion and bought a 2003 Suburban Z71 with a 5.3L.
I've owned the Suburban for over a year now and I love it. I haven't done much work to it (although my first trip out of town the radiator blew up on me), and the work I have done has been cheaper than the Excursion. I also love that there are so many parts out there for these vehicles. I went to the junkyard recently and looked through a ton of Escalades, Yukons, Tahoes, Suburbans, etc; It was nice to have so many options.
The OP mentioned wanting to get into a Diesel. I would love to see someone get a 2500 suburban and drop a 6.6 Duramax in it. I assume it wouldn't be too difficult since the Silverados have the 6.6s and the engine size is the same.