cant decide on p or j so i would like to hear why you would rather own a jazz bass.
On the other hand why you would rather own a p bass??
They're two different animals - I subscribe to the school of thought that includes having at least one of everything.

Even though I do NOT have one of everything - I currently own an American Vintage Reissue 1957 P bass, a Mexican fretless Jazz Standard, and a circa 1986 Peavey Patriot that I bought new when I was a teenager. My P bass is the only one I take out to gigs with my current band; it projects a whole different attitude than a Jazz bass, and I'd have to say the Precision will always from now on be my "number one." I'll always have room for a Jazz though, and if I had unlimited funds, I'd have two of each, maybe three, plus single coil P basses, Stingrays, Gibsons, G&Ls, and more. Some strung with flats, some with rounds, some active, some five string, some four string, etc.
The P bass for me sits in the mix with an attitude. It's rarely there to be polite, it is there to be the "dad" of the mix - the old reliable, the star by which everyone else navigates their part, the foundation of all, not to be bargained with or negotiated with, stern when needed and friendly and caring when needed, the provider, the balls of the mix, the hair and muscle of the arrangement, the glue of the family, the wind beneath their wings. It needs to be approached and played that way too - if you don't like a P bass, you just don't understand a P bass.
The Jazz for me is a different animal altogether. It is really very much more like a "bass guitar" than a bass - there to provide the harmonic fundamental to the mix, for sure, but also meant to and more able to leap and jump around nimbly through the arrangement while doing so. I mostly played a Jazz when I was doing a duo gig with my singer/acoustic guitar player - no drums and no electric guitar, and he can't play lead, so I had to create a lot of energy in the mix that was otherwise lacking - not necessarily by being busy, but by taking control of the arrangement in a way that would have been different had I been playing a P bass. The bridge pickup allows for some variation of tone and can be shifted on the fly in a way that is quite different from a P bass. It is true that a P bass can offer a wide variety of tones by shifting right hand position and technique, but the same is also true of a Jazz bass - plus you also get the variety of tones provided by backing off the neck pickup and bumping up the bridge pickup. This can be very handy when simultaneously filling multiple "roles" or voices in an arrangement. A Jazz seems to be more able to stand out in a mix, at least with typical EQing, technique and strings.
Sometimes you need a bass that helps you stand out, sometimes you need a bass that helps you hold everyone together.