If someone told me I could only use my choice of Xbox controller or Guitar Hero guitar, I'd give the guitar a shot. Dualshock 3 and 4 have their merits with a good d-pad, but Xbox's is worse, and I dislike using my thumb for four buttons.
Fightsticks aren't my controller of choice either. I use a hitbox, because I like keyboard. But hitboxes are expensive. The Mayflash F300 Fightstick is $60 and works on everything (on PS4 you'll need a regular controller to connect to the stick, but it's no concern on PC).
Keyboards do have the potential problem of key ghosting. Triple-button presses not registering, making it impossible to do backgrabs, most of Beowulf's hype moves, and much trickier to do Blockbusters. Depends on the keyboard, and mechanical keyboards never have this problem. You may also have fat fingers, in which case yeah, you should probably use something else.
Aside from that last case, it's probably not the keyboard when it comes to a regular combo. It took me days to be consistent with Filia's full-Undizzy universal combo, and that was after breaking it down some and using slow-mo to figure out some of the timings because I can't mash all of it (just most of it). And that's a relatively simple combo, Parasoul's universal combos are harder. I don't know about your characters, I haven't tried them.
