What type of tuba is the best? Bb...Eb...C or F??

The answer probably depends on the type of ensemble and at times the music. Although using a different mouthpiece can make a big difference and there is also significant variation between manufacturers and models.

In a UK Brass band, we only have EEb and BBb tubas or basses as we call them. The favoured model is the Besson sovereign which has an instrinsically mellow tone (especially the BBb) ie the higher harmonics tend to be suppressed.

In Symphonic Orchestras F tubas have been historically favoured by some people but today a greater range of instruments is used (especially in amateur orchestras). I believe CC tubas are fashionable in the USA. Personally, I find a EEb a better all round choice.

Here where I live people start on contrabass BBb, and most often switch to CC in college. Bass tuba in F is used a lot in symphonic setting.