I recommend following common tubes/brands basis my experiences & understanding:
- 12AX7 (ECC83), 12AU7 (ECC82): Mullard/Philips/Valvo (Made in Great Britain/Holland) for open & clean sound rich in 2nd harmonics
- 12AT7 (ECC81): Nothing can beat RCA, simply the best sounding, these tubes are normally used in the phase splitter section of a push-pull amp.
- EF86: Mullard, Low microphonics, very warm and clean
- EL34: Mullard/Philips/Matsushita for Guitar Amps, Mullard/Golden Dragon for Hi-Fi Amps
LONG PLATES VS. SHORT PLATES
The 12AX7/ECC83 the most popular preamp tube comes in two main types: 17mm Long Plates and 14mm Short Plates. These include tubes were the first produced versions and are costlier than others. Short plate 12ax7 tubes were first produced by RCA, GE etc. and and later on by Philips, Mullard, etc. The idea behind short plates was to increase longevity & decrease microphonics.
So far as sound is concerned as intuitively appears, Long plates are mode open, sound-stage is much wider than short plates, however, they are inherently microphonic. Short plates are more suitable for Guitar amps for now obvious reasons.
BLACK VS. GRAY PLATES
The first produced 12AX7 were Black Plates, the gray ones were subsequently produced. In general, black plates have more warmth, more 2nd order harmonic and open sound than gray plates.