I haven't heard the new Mullards, but in my experience, the tubes out of Sensor (Mullard, Tung-Sol, and Svetlana reissues plus the Winged C's) have been more reliable than the Tesla JJ's of late. If you're referring to the older, pre-JJ Teslas, then I'd go in that direction. Otherwise I'd try to find a good deal on the winged C's or if that's out of your budget, I haven't heard anything bad about the New Mullards. I do think the JJ/Teslas sound good (they've got nice, clear highs), but I've had them fail and I know a lot of people who have had pin issues and other failings.
I personally use NOS Svetlanas, Siemens, and RCAs, but just ordered a set of the Shuguang Treasure 6CA7-Z after getting a bunch of very strong recommendations.
What sound are you looking for? IIRC the mini-mites don't require any adjustment to use KT-88/KT-66/KT-90/KT-77/6550's. If you're looking for more bass and less of the euphonic midrange, you might want to consider KT-88's.
Good luck