Fastest validation query in PostgreSQL
This is obviously nonsense. SELECT 1 is faster (if only by a tiny bit). version() also returns quite a few bytes of text, in my case:

PostgreSQL 9.1.2 on x86_64-unknown-linux-gnu, compiled by gcc-4.4.real (Debian 4.4.5-8) 4.4.5, 64-bit


So you get some additional I/O, too.
pgAdmin, for instance, uses SELECT 1 as validation query.