Rise of the Reds is my favorite, but Shockwave and Contra are also pretty good. Only issue I have is the performance takes a hit since the game is so heavily single threaded and the game logic is tied to the frame rate. Luckily there are a couple projects trying to alleviate that but they’re a long way from being ready. OpenSage and Thyme specifically. GenLauncher is helpful for trying out the different mods at least.

I usually end up just playing Zero Hour with a few GenTool modifications though.