Hmmm depends on how much money you wanna spend. Since you're only changing V1 you may as well throw down a little more cash and get something nice that will really make a difference. If you've got about $50 you can get a Raytheon black plate 12ax7, better than RCAs IMO. Also there's the Preferred Series 7025 (super durable) from the tube store, an exact replica of the most sought after NOS Mullards from the 1960s. There are literally thousands of great options, I say go NOS for sure, otherwise you can just get your basic EHX or Sovteks, but if you're only changing V1 I say go all out!
Edit
Sorry didn't read your first post carefully, I see you've got options. The EHX will have the least microphonics, the Sovtek will probably last the longest, and the Mullard will most likely sound the best. But all tubes are unique, even the exact same make and model, so your mileage may vary.
