i have a jl 500/1 amp and had 2 10" niche audio 4 ohm subs but they just gave out( they were used )} in a sealed box (this is a f150 4 dr) i was thinking about replacing them with 2 kicker cvt10 not sure if 2 or 4 ohm or maybe some other sub need some info what will sound better?
Well, your budget seems to be around $300 for both subs (assuming u can afford CVT 10's). And I assumed u needed shallow-mount subs until I went to Niche Audio's site and didn't see any shallow-mount subs available (if I'm not mistaken).
So I'd look into some AudioQue SDC2.510's ($129ea.)
Just don't get crazy with the gain after seeing that you can put 1200 watts to them and crank up your HU without first tuning your 500/1 (which, sadly, will only provide less than half of what they can handle).
Oh, and of course be sure of the enclosure size that you're putting them in.
...and down the road when u get the funds, upgrade your amp.
(This is all assuming that u want to continue to use two 10's and want to keep using your JL 500/1.)