That is a personal answer. I know many people who play other MMOs instead of WoW because they enjoy them more. I myself play 3 MMOs right now, all at a more casual level. I enjoy all of them.
If you mean subs, then there are MMOs out there that already rival wow in active players, they are just F2P.
F2P is where most games go, so it is not likely that another sub based game will have the player base WoW does.
Does this make WoW better?
That is up to you. There is no better game. It is all a personal choice.
I always recomend people play other games. be it other MMOs or just other games in general. If they have the time of course.