Funnily enough I have gone from 4 (my first 15 years) to 5 (for the last 13 years), to 6 (for a few years) and now mostly I am back to 4, although I do need a 5-er for some of my dep gigs and if I do not know what to expect I use take the 5.
In all instances I like 18.5-20mm spacing (so like a TRB :)...) regardless if they are 4,5 or 6. Less feels "cramped" (not that it really impact my playing though, but the muscle memory is very much geared towards those spacings.
Horses for courses right?