Tele ECC82 smooth plate - lots of air, very clean, transparent, lots of bloom, very liquid sound, strong sense of palpable image. Nice tall soundstage - the instruments have great bloom.
RCA clear top 12AU7 - very musical and dimensional, but not my favorite in the 303-300
Siemens 1960's ECC82 (called chrome plates, but I think it may be nickel) - shiny plates, very palpable, very textured mid-range, nice holographic soundstage and deep taut bass
Tele ECC802S - my overall favorite, it just does everything right, has the tallest, widest soundstage. All sound and ambient cues just fall in place. The music flows, simply flows.
Valvo E80CC - very liquid bass, mid-bass and mid-range, sounds a bit rolled off from the mids up
Amperex PQ 6085 (E80CC) - wow, these have the nice bass, mids and liquid sound and a nice high end, lacks a little of the soundstaging of the Tele ECC802S, but still very very nice
RT (RadioTechnique French govt/military 1960s) 12AU7 - lots of air, lots of subtle ambient cues, very good sound, these are really nice too
Tube rolling is a must to get the best performance from this player.
Also, I recommend using the balanced outputs if you can.
And yes, bypassing the preamp and driving the amps directly results in a more transparent sound, more immediate/palpable.
