Hi, I would like to buy a mustang bass and I have three options.
1. used MIJ Fender Mustang in white for 700 Euros (about 795 US dollar)
2. JMJ Mustang
3. American Performer Mustang
which option would you choose and why?
I’d choose the used MIJ Fender Mustang in white because that’s what I actually
did choose, and I’m happy with my choice

That said, back when I got it, there was no American Performer Mustang and the PJ wasn’t widely available yet.
The PJ could still intrigue me, especially in a Surf Green-type finish, perhaps.
My thoughts on each are:
MIJ - awesome little bass. Love the "slightly quirky classic" aspect, without the hassles of getting/keeping a true vintage instrument. Nice P-like tone, but a bit thinner/less-full sounding than a P. Sometimes I do wish it were fuller sounding, but once the group gets going it sounds absolutely fine (read: good). Love the one pickup aspect: Plug it in, tune up and start playing and it just sounds good. Love the narrow Jazz-style neck, but if there were one thing I could change about it, I’d get a modern 9.5" (or heck, 12") radius fretboard. I like the string-through-body bridge so that I can use regular scale length string sets. I find the thinner frets a nice vintage-style touch
MIM PJ - having a full-sized P pickup is intriguing. Personally, I’d rather there were no J pickup. The (famously scratchy) pickup selector switch on these could be good for quickly going from the neck to an alternate ‘both pickups’ sound, but my main use for the bridge pickup on my Jazz, for instance, is just to dial in a hair of bridge to my full on neck sound to add some clarity. I almost never use a "both pickups equal" sound, and never use the bridge soloed. I like the 9.5" radius on these. Top loader only bridge means string selection is more limited than with an MIJ. No more rosewood fingerboards. The price is nice on these...
MIA American Performer - I like the wood on the sunburst. With the MIJs and vintage Mustangs, the wood under the sunburst looks cheap/unattractive, imo, but the sunbursts on the American Performers are quite nice. A surf green could be sweet, too. I wish it just had the Mustang pickup though — I really have no need for the J, and in fact having it there just adds a distraction for me. Since the J is there, I’d probably like this VVT control setup better than the PJ’s selector switch, but as I’ve never had a bass with a selector switch before, i can’t say for sure. P-width neck wouldn’t be my first choice, but as my main bass is a P, it’s not exactly a dealbreaker for me. 9.5" radius is good. I think the bridge is top-loading only? Price is not cheap
JMJ - I like the traditional single pickup on these, and people say the JMJ’s pickup sounds quite good. The big flaw for me is the reliced finish. It’s not bad, but I’m not one for the pre-aged "roadworn" look. What finish there is is nitro though, so...I dunno. P-width neck, again not my first choice, but I’m fine with that. 9.5" radius.
None of them are quite my dream Mustang, so each involve some measure of compromise for me. However, the Mustang is a great platform in general. Basically, they all seem pretty cool to me, and I’d be happy with any one of them