Sweetwater. If they carry it, I buy it there, even if it's a few bucks more than somewhere else. They take care of their customers, in my experience.
Just one stupid example, even though it isn't studio gear: I wanted
a Vox AC15 re-issue about 5 years ago, but it seemed that so many of those amps were lemons. They ended up discontinuing them, as a matter of fact. But I played one in a shop, and it seemed like a perfect studio amp...low wattage, master volume, Line Out, etc, great classic AC30 type tones, but better for recording. But even the shop model had a crazy rattle when you turned it up.
So I called the guy who handles my business at Sweetwater(that's another thing, you deal with the same guy all the time, they assign your account to an actual person) and asked him about it. He called the amp tech down in the basement or whatever, and the guy pulled one from stock, opened it up, tested all the solder joints and tube sockets, put rubber washers on the reverb tank to prevent the rattle, junked the crap Chinese tubes and put in matched and tested Electro-Harmonix tubes, and generally made sure it was solid. That amp is my workhorse, played every day for 5 years without a single problem. If you ask around, 9 out of 10 times people will say that model was unreliable junk.
With the exception of cable and connectors(markertek rules on that), pretty much everything in my studio came from Sweetwater, unless it was something they just don't carry, which is rare.
And no, I don't work for them.