Definitely 8 man. 7 and 8 are similar gameplay-wise, but 8's Master League has more depth. Players have "life spans", so balancing between young improve-able characters and older pro's is a must. Also there's more animations which are definitely noticeable, like fouls. 8 is more of a 7.75 cause the graphics and gameplay (more fluid moves, or more moves in general) aren't as improved as 7 over 6 was. But you can tell they really spent more time improving ML mode so it has more longetivity. I've played since 6, and have always managed to stay interested in my ML team from the day of release, to the release of the next edition. But considering the improved experience system, and the huge increase in teams (most official btw, much improved over 7), I can tell 8 will hold my attention for much longer.
People say the WE series as a whole is more "hardcore" or detailed than FIFA, but it's not necessarily difficult to play in my opinion. Like Virtua Fighter 4 Evo, the training/practice drills/matches (if you wanna do the cup modes, etc.) will slowly build your skill so that soon you can start moving the difficulty up and up.
hope that helps. sometimes the PC version is cheaper (i know WE7 for PC is now $20 at Fry's), tho u might have to wait a bit for WE8 (PC) to drop.