6x9 or 6.5

Hey, my car have 6.5" stock in the front door and 6x9 stock in the rear deck. I want to know if its better to buy an adaptor 6x9 to 6.5" and buy 2 sets of same speakers or stay with 6x9?

I would'nt say having the two same set of speakers are better than to different sizes with 2 different brands.  I would stick with the existing sizes your vehicle is equiped with.  If anything, I would, and did modify my stock fittings from a 6.5 in the rear to a 6X9. 

Sonically, it makes sense to stick with the same speaker line if they use the same technology in the tweeters, etc. They will blend better. On the other hand, rear speakers provide fill more than anything. They don't set up the front soundstage where those 6.5" will. The front doors will be more important than the rear deck. It all depends on budget, application, etc. If you're just replacing speakers and want to keep it simple, stick with the stock sizes but buy from the same line/brand of speaker. Concentrate on the 6.5" being your quality speaker up front versus the 6x9 in the rear. If this will be amplified by a separate amp, it's a different story. I think we need some more info like is it a stock H.U. or aftermarket? What kind of vehicle? Will any of the speakers run on a separate amplifier?

Golf has you on the right track.... I opt to swapping a 6x9 to a 5-1/4 in the rear. Especially in a rear deck situation when it fires straight into the back window. The more info of the environment the better answer you can get though. Unless it matters not to you, then whateva is cleva.This is what I do for FUN!