+1 The P5Q Pro is excellent--I use one myself.
However, I recommended the better Asus boards to you because from your very limited information (you did say "best"), I inferred that you would be going long-term (e.g. 5+ years) and maxing out the LGA 775 platform.
The P5Q Pro is best if you're on a budget.
The P5Q-E is better than the P5Q Pro because the E has a better cooling design in general and especially for the MOSFETs around the CPU (better for OC). It is also a better quality board, if you don't mind spending more.
The P5Q Deluxe adds 16 phase power (same as on the Maximus II Formula) to the E, so if you want the highest and most stable overclock, that is the one to use.
This would last you well through Windows 7, IMO.
Btw, if you haven't already purchased your Q9450, I would go with the Q9550 for 0.5 higher multiplier or the Q9400 for the same multiplier but higher R0 stepping. The Q9450 is not a very compelling buy, IMO.