gentlemen or gentleadies if applicable...
If you want big sound... you'll need to go with 6.5 in the front, but technically 6.5 inch speakers in the front don't REALLY fit, you'll have to do without the stock grilles, they have to be relatively low profile 6.5 too, Alpines don't work because they're 6.5 has this weird mounting ring, neither do Hertz as they're too deep.
If you want to go with the stock grills, best advice is modify the stock speaker mount, by grinding off the original speaker and mounting the speaker to the metal rings that came attached to the speaker, in this case you may be able to swing SOME 5.25 low profile. Some brands that work besides Pioneer, are some Kenwoods and some Kickers. 1 13/16 is as far as will work in the front, but will touch the window guide.
Please do your research, as I wasted a ton of time looking for what sounded well first and then it wouldn't fit in my car.
I have the kicker 5.25 in the front, they sound good, if you really want bigger sound, think of getting a small amp put in where the stock amp is to power the setup, or of course getting a 4 channel amp.