I replaced the stock pickup in my Fender P with a Bartolini 8S. It was a big improvement. More output, better clarity, warmer tone. It's especially good with flatwounds.
I'm sure the Bart 8s is a good pickup, in fact I may try one one of these days myself - but what sound are you looking for? There are a ton of good pickups on the market, each with its own personality. Also, why don't you like the stocker? Is it MIM or MIA or MIJ?
oh sorry, its a MIM fender, im basically looking for more output and better low end/punch i like the overall tone of the stock, so im not looking for a huge change; just more low end as its weak on the stock pickup
I had CBS Precis for a very short while. I put some Seymour Duncan Bassline Quarter Pounders in it and it made that thing "born again." Would never replace my pre-CBS though.
Like I say, I haven't tried the Bartolini 8S. It might be just what you're looking for. However, I have tried both the Basslines SPB-2 Hot, and the SPB-3 Quarter Pound. I prefer the SPB-2. Plenty of output, and a smoother top end than the Quarter Pound. The Quarter Pound has a lot more highs, and while it was OK, it seemed a little clicky to me. Either one is probably a lot better than the stock MIM pickup, but I like the Hot better for the deep, thumpy sound. I can get good definition from it as well. If you just want the classic P-Bass tone, you might try the Fender Original 62 pickup. It also seems to get good reviews.
I was going to put the Bart 8S in my '75 P largely because of my positive experience with Barts in my Jazz. But somebody suggested I take a flyer on Rio Grande Replacement for P.....so I did. I love the result. A little more output but much bigger bottom, "toppier" highs and fabulous all around clarity and balance. I'm very sure I would have been happy with the Barts but now I'll never know.