Typically threads like these are deleted, since removal of emissions equipment is against Federal Law, regardless of local requirements. However since you're seeking advice on how to rectify the situation, I feel it's prudent to leave it open.
Magnaflow cats tend to offer the best bang for the buck.
Since you've removed the cats in the y-pipe you will need to ensure you install at least one 3 way catalyst to address NOX. Since the 4.0 does not use an EGR valve, a 3 way catalyst is used to keep NOX levels in check. This would then be followed by a traditional 2 way catalyst further down the exhaust stream.
Also, FWIW, cat vs. no cat really doesn't make much of a difference in HP. I'd be surprised if there was a 5HP difference on a mostly stock 4.0.
'00 WJ 4.7 Limited- Some stuff
'03 WJ 4.7 Laredo- Some more stuff
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It is what Jeeples has *PARTIALLY* stated.