I think it also might not hurt to have a starting point for reference. I think I replaced my first pickup around when Vai signed with Ibanez, and I've probably owned 30 or 40 different pickups since then, and now I have my handful of favorites (Important Side Note: I use different pickups for different overall applications, there's no swiss army knife for tone) but even though I have my favorites, I'm still always finding out surprising things about what I want for myself in my own tone. I think that goes for everyone.
I'll get egged for my first suggestion, but if you have a paul and you like rock and metal, toss in a Gibson Dirty Fingers. It's what I've played forever, it's what I use for 90% of everything, from classic rock to 80s hair rock to prog metal to scoop metal. Another alternative is a Duncan Distortion.
Now that I'm dripping with egg yolks, I'll say why I pitched a couple non-BKP pups. They're not too expensive, and I think it will be really good to get a first respectable aftermarket pickup, so you can say, I like the Dirty Fingers, but I would like something warmer. Or cleaner. Or lower output. Or a little more scoopy. THEN, your favorite mates on the BKP board can suggest a dozen different things based entirely on your specific critique of your own tone.
I think you'll find over time you'll want a Nailbomb for metal, a Cold Sweat for Randy, and a Miracle Man for Ozzy and Black Label. And maybe mules for classic rock. Who knows. But you have to jump in some place, and no one pickup will do it all.