The Fender '57/'62 might be the best Stratocaster pickup upgrade
You have a ton of options where Strat pickup upgrades are concerned, but this pickup set rises above the rest.
When it comes to Strats, there are 3 things I prefer.
First, I favor the SSS pickup configuration most where all 3 pickups are single-coil. Yes, there are "hot rail" pickups for Strats (which can be had for fairly cheap these days) that are humbuckers, but that's not what I'm talking about. What I'm referring to are true singles.
Second, I greatly favor the classic look of exposed pole pieces.
Third, I favor pickups with good output, but not so loud that it's an unmanageable mess.
The Fender Original '57/'62 Strat Pickup set seen above meets all these requirements. And, fortunately, it is not the most expensive pickup set for a Strat Fender sells. (For the curious, the most expensive Strat pickup set by Fender sold right now is the Eric Johnson Signature.) It's a set that Fender states was reverse-engineered out of a '63 Stratocaster. What you get is a blend of '57 and '62 voicing...
...and this is the kind of clean tone Strat players go for:
What ultimately matters on a Strat is how good the clean tone is because that's your foundation. If the guitar sounds good clean, you know it will sound good overdriven or distorted later. You also know it will take well to effects such as reverb and delay.
This set has been out for a while now, and oh yeah, it's good. Definitely gets my stamp of approval.