What is the best premp for Atma-Sphere MA-1 3.3 amp?

Atmasphere MP3 would be perfect match for an Atmasphere amp. I find the 6SN7 tubes in any pre to sound fantastic. I've been using an MP3 for a while without a hiccup.

Another vote for the MP-3.  I own and have been using an MP-1 with M60s for almost 20 years now. A close friend/audio bud has been using an MP-3 with MA-1s for about 10 years now. We have swapped preamps several times and I'm here to tell you that IME, the MP-3 gives me, minimally, 90% of the performance I get with the MP-1. It's probably even closer than that. In all that time, neither of us has had a failure beyond the odd tube giving up, whether it be amp or preamp. And Ralph and his staff are always available to assist you over the phone and will spend all day with you if the situation demands it. Honestly, I don't know how they ever get any product out the door considering how generous they are with their time. Truly a no brainer...go for it.

thank you all for your comments. If MP-3 is 90% of MP-1, I doubt my ears can tell the difference. Then the question is, are you comparing version .3's? Or is there not that much difference between MK3 vs. MK3.3?

@chungjh check out Audioasylum trader there's a sealed MP3 mk3.3 for sale. 

@OP, 
I PM'd you, but didn't indicate the build model.
I own the 3.3 version MP-3.
Also, when I called Atma to inquire about upgrading the MP-3, he said the 3.3 was an entirely different build from earlier models, and to upgrade an earlier model would cost a significant sum. You can see the prices on Atma-Sphere's website.
BTW, one of the reasons you find so many satisfied Atma customers is that you are only a phone call away from help, should you encounter an issue. Most likely it will be Ralph answering the phone, and most likely it won't be the Atma causing the problem- believe me, I know.
Bob