Keep it simple. If you want to try some extremes of look, I'd start with Rodinal and Xtol. There are pretty much as opposite ends. If you prefer the look of Xtol, you want a fine grain developer. If Rodinal, look toward things like Acufine and and gritty. Personally, I like Xtol for 400 speed and up 35mm film and Tmax 400 in 6cx6 and Rodinal for Acros in med format or 35mm. Honestly, I can't a huge difference between xtol and D76 or even HC110. For me, the most important thing is to make sure your stock is always fresh. That leans toward HC110 and Rodinal. Xtol stored in full glass bottles (I use 5 1-liter brown Boston rounds from SKS) last at least 6 months or even a year