head/tail are nicer than first/rest because head/tail are both four characters, thus code can line up more nicely. size might win over length for its similar length, although len() has its appeal as well. fst/snd I think are too abbreviated, but I appreciate their brevity.
Instead of first/rest a syntax like x[0], x[1:] might make sense - these call get(0) and getFrom(0), and then no head/tail methods are needed - however, I think head/tail reads better than brackets.