WA33 is probably the best tube-based option. If your preferences run Solid State I'd consider the HeadAmp GS-X mk2, and if aesthetics don't matter to you, the Audio-GD Master 9.
TOTL Headphone Amps
Looking for some feedback on what TOTL headphone amps people are using. I used a Auralic Taurus MkII for a couple years, and I'm currently using a Rogue Audio RH-5. I'm considering moving on to a Moon 430HA. Has anyone tried the 430HA and RH-5? Are there other headphone amps in this price range that I should be considering?