Canonical's policy is to release an updated version in April and October
every years. Long Term Support releases come every 2 years in April, i.e.
April 2008, 2010, 2012 etc. They have full, free support from Canonical for
3 years - bug and security fixes and software updates. All normal releases
are considered "Stable" but (obviously) some are better than others and they
get 18 months of full, free support.

Unless you have a huge amount of RAM (3 GB +) the 64 bit version won't make
much difference and the 32 bit versions are a little better supported. I'm
running 64 Bit on one computer and will probably go back to 32 bit next time
as I "only" have 2 GB of RAM and see no benefit to it.