I think the Telemaster would probably deliver the most instant gratification. Not just because it's a Tele and all, but because it looks to be something you could be playing almost immediately. The Jagmaster could be just as quick if your just dropping the p'ups in, but if you have to wire and set up the numerous switches for it, ugh. That doesn't appeal to
me. You might be better at soldering though and it might not be an issue. The JagBass does look fun, but it has the most potential to be frustrating and could loose the fun factor very quickly. It could also become one of the most fun things you do this summer so it's still a toss up.
My vote: (for what it's worth)
Telemaster
Jagmaster refit
Jaguar Bass VI conversion
Any way you go, it looks like you'll have fun this summer!