To the stick vs pad debate -
SF4 is, as well as many other fighters are, designed for arcade play. Their inputs are designed for an arcade stick to input them. When translated to a pad, it is hit and miss. Some characters are able to be played well on a pad, many though suffer.. and some are damn right impossible.
C.Viper is infinitely easier on a stick than on a pad because the stick allows a very quick chain of inputs which require accuracy. We're not talking mashing out srk's or throwing shoryukens.. we're talking about fd, fd pp, db, ub, db, b k, db, b p, df, df, f ppp.
Also many techniques such as jump in options / buffering, kara moves, plinking links, and negative edge are actually very easy and natural on a stick, but on a pad are a nightmare..