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Depends what you need, if you need a tank, 2 is your best bet, it's got amazing defences and with recover never dies. Now, if you need a glass cannon, Zed is your best choice, but he's fragile as fuck and will require assistance to really be able to put out as much power as possible, generally double screens or a sub to let him get a free hit in (unless he's up against some fuck with Hyper Voice).
2's build is fairly well known, but as for Zed I like to set him up with Adaptability, splitting EVs in Speed and SpA, Nasty Plot, Dark Pulse, HP Fighting, and Tri-Attack, with a Life Orb, then set him up with screens from a teammate with Light Clay, then switch him in and commence sweeping. He's quite fragile still, however, so he still gets rekt by mach punch and faster fighting types, but anything he does hit, he hits like a freight train, OHKOing a lot of enemies, and even 2HKOing a blissey after one Nasty Plot.