Time for new tubes.. which ones?

My TAD-150 preamp which has only 2 tubes stays on all the time, so every year I have to replace the tubes. This is my first time replacing them. Does anyone have an opinion as to what tube to use, or should I just use the same replacement ones from TAD? I would like to improve the sound if possible with new tubes. Thanks
12UA7s are a big thing in a small tube. I am using mullards and the are a great improvement over the Chinese tubes that came with my McIntosh 2102 amp.
what are you trying to create sonically ??

different tubes have different presentations.
The Cryoed 12AX7 were not as good as I had hoped. The Cryoed 5814 Sylvanias sounded very, very nice but did not have quite enough gain. So much for the Cryoed ones for now.

I currently have GE 5 Star 6201 in there and they have impressed me. 6201 are military spec 12AT7. They bettered some Raytheon 12AT7WA I had. For want of a better term the 6201 had a more "spacious" sound (larger soundstage and more air around the intruments) then the 12AT7.

The GE 6201 were 20 bucks for a quad on EBay. I have some Sylvania and Mullard 6201 en route from Upscale Audio.

I'd say stay away from 12AX7 as you don't need the gain with the TAD150. Use a 5751 instead (military spec 12AX7 with lower gain, similiar to a 12AT7). Since the pre comes with a 12AT7 it might be best to stay with them (12AT7WA, 6201, 7728, ECC801). If a 12AU7 gives you enough gain you can use them (5814, 6189, 7730, ECC802).

I had asked Paul @ Bizzybee about 5751 and 5814 and he said they would be good choices. He does not believe in leaving the TAD150 on 24/7. I use mine with an Odyssey Stratos Extreme that I leave on all the time but turn the TAD150 off when not in use.
I have gone a bit tube crazier and have brought in several more to try
12ax7 RCA black long plates D getters-good air and soundstage in the can't go wrong with (CGRW) it category
5963 RCA long black plate D getters-also very nice, a little sweeter presentaion than above a tad less detailed
Amperex Bugle Boy 12at7 (made in France w/music clef on the side, big round getters-cream of the crop so far, for my preferences-very fine detail and air but tends towards brightness
Tele 12au7 ribbed plates-very well balanced sound does most things well, very livable
Amperex 12au7 med grey plates world logo-very interesting tube to audition finely detailed nice soundstage but may be brighter than some tastes allow.
I have some 5814 Sylvanias to get into the mix. I still would like to get a pair of tele12ax7 to try

Some of the CGRW others
Sylvania 12au7tw and 7twa
Sylvania 5751 grey plates-Tripple Mica
GT12ax7m gold series

Not making the cut
Mullard 12ax7 short plates
Mullard 12au7 short plates(better than the above Mullard)