For me you can't beat a Strat through a Fender Twin Reverb. That's about the best clean there is. But I'm not wild about MOST Fender amps when they're over-driven, or when they're used with Les Pauls or other humbucker-equipped guitars so I doubt I'll ever buy one. Maybe a Bassman someday.

For cleans on both single-coil AND humbucker guitars I really like the Vox AC30 Custom Classic 1x12 I owned up until recently. I sold it a year ago to the rhythm guitarist in one of my bands; but that's a really sweet amp for the money. I find it's nice and sparkly and chimey with a Strat but handles those growly Les Paul lows pretty well too.

If you want to improve your clean tone regardless of whatever amp you're using; go out and get a Keeley Compressor.