The other guitarist in my band just got a 5150, and it sounds great with my Mark III in the mix. The 5150 has more low mids and a bit more modern sounding tone, while the Mark III has more of a high mid crunchy tone; works great since I'm the lead player and I like to have my tone cut through just a bit more. He used to use the Ibanez Thermion head, which is a decent amp, but it didn't cut enough in the band mix, my Mark III just buried it. The 5150 hold it's own very nicely. He also sounded very, very good when he used my Mesa Studio Preamp/Recto 2:100 rack; it sat perfectly in the band mix.
So I'd say either a 5150 or a Dual recto. The DC-5 is also a great amp that would match up well with the Mark III and is a bit cheaper, if you can find one. And it would be much better if he can get his own cab, a 2x12 would be fine.