Any means of getting rid of the restrictive Y-pipe will provide the best performance (and usually better sound). So that leaves a full dual exhaust system (with X-pipe or H-pipe) or just true duals. True duals would have to be custom from a shop (since nobody makes kits), so I say "Get custom true duals!"
If you really wanna go crazy: some companies offer hot-rod kits, where it's a bunch of different mandrel-bent tube pieces to custom route your exhaust. Then you could do side exhaust, center exhaust, or any other way of exiting... but you might affect sound, I'm just not sure how much?

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YELLOW JACKET = 1998 Chrome Yellow V6
POWER: BBK CAI, TB, UDPs; Bosch Platinum +4 plugs
BEAUTY: black projector headlights, taillights, and mesh grille; 5% tint; shorty antenna; interior billet
ROLLERS: XXR 006 black spoke with blue lip; 18x8.5 & 9.5; BFG KDW/2 245/40R18 & 275/35R18
DRIVER: Jonathan, 6'2, 190 lbs
RIDER: my wife, 5'4 brunette hottie

and my 1st baby on the way...
