I have not played with any of these players in except just when messing about...All of them are quality, with bale he can play multiple positions, even sb, swb, so forth that gives you a chance to acquire someone else...
Johnson, to me has always a be a bright spot since he came to man city, he was one of those players I discovered on my own and said he would be great...he is very skillyful great at attacking and playing amf, smf, sometimes cm...he's one of those players u want dictating your offense
Lennon- Very fast thats about it, has good skills, but you cant really move him outside of his rm/lm, rwf/lwf, smf type of position...he is small he tends to get muscled off the ball easier especially in this years konami as the strength of players proves key at times...
Walcott- Same as Lennon if not has greater potential to be absolute beast...he can shoot and has a nose for goal...
These are just my opinions as I have played with them messing about and thats how I looked at each person, I think you would get more for your buck by going with Bale of Johnson just because of the different positions especially with Bale he can play for you.