I agree, it's definitely an element of preference. I personally have Fralin P-90's in a '72 Tele Deluxe RI, and they sound great. Ultimately, it's a function of what tone you want, what guitar they go into, and whether you want humbuckers or true single coils. There are P-90 pickups available in the same size as a standard Gibson humbucker, there are stacked humbucker versions, but the original P-90 is a single-coil pickup that is bigger than a standard Fender single-coil but smaller than a humbucker.
...and if you don't like it, you can suck on an egg.
Comments
I personally like harmonic design, lindy fralin, and seymour duncan, but gibson makes fine P-90's as well. Rio Grande has a nice set too.