Well WM or IF depends on your class, surely. For example, you are an archer, you better choose WM for more archery, so more accurary. If you are 2hander, choose IF, because you get more hits and bumps etc than a hiding archer. With 4 WM at e.g. 2h, you have at level 30 around 140 WPF, shall be enough. So, you want to be faster/have better accurary, choose WM.
You want to be able to get more hits? you often get bumped/teamhittted or archers shoot you?? Choose IF!! But decide, what fits better to you. Maybe you can split your last points to both (how much you have left).
As Shielder I would take WM, if you have less than 4. I would choose IF at shielder, if you have less than 3or4. So Melee IF, ranged indeed WM. As Lancer, or cav, I woupd split it.
Hope I could help YOU!:)
Greetings.