What variations in particular are you finding difficult to meet? The 4...Nf6 5.Nxc6 variation is pretty sharp, and requires concrete theroetical knowledge by both sides, but 5.Nc3 (the Scotch Four Knights) is a lot simpler to play, and not necessarily worse. You can meet 4...Bc5 in a number of ways but the trendy 5.Nb3 Bb6 6.Nc3 and 7.Qe2 variation might be the simplest (there's also 5.Nxc6 Qf6 6.Qf3 if you like to exchange the queens early). Finally for lines like 4...Qh4 you just have to do your homework and learn the antidote - starting with 5.Nc3 Bb4 6.Be2 Qxe4 7.Ndb5 Bxc3 8.bxc3 Kd8 9.0-0. 

You'll progress with any reasonable opening if you learn it properly.