It depends on the location. You can't really say which one is better.
I own Smart and Globe. I live in Baguio.
On some locations one of them would not work, but on another location, the other provider would be better.
For most places in Baguio, Smart is the best to have. Mas malaki ang coverage. Even if I drive out doon sa may boundaries and adjoining provinces may signal pa ang Smart. Yung Globe wala na.
Globe only works well kung nasa city proper/business district and could be faster than Smart. Beyond that place, mahina na ang Globe.
So you see, depending on the location, I could just say one or the other really sucks!
I haven't tried Sun, but I've read a lot of positive feedback from those users who actually used it here.
But if you really need a stable internet, don't get a plug and play ones. Better pay monthly for the wired internet ones from PLDT, Bayantel, GlobeDSL, etc. They work even in adverse weather.