For travel times you mention in your post, here is how various UY months would "work" (using 2009 UY in examples) :
February 2009 Use Year : points available Feb 1 2009 - Jan 31 2010
must bank by Sept 30 2009 latest
March 2009 Use Year : points available Mar 1 2009 - Feb 28 2010
must bank by Oct 31 2009 latest
April 2009 Use Year : points available Apr 1 2009 - Mar 31 2010
must bank by Nov 30 2009 latest
June 2009 Use Year : points available Jun 1 2009 - May 31 2010
must bank by Jan 31 2010
August 2009 Use Year : points available Aug 1 2009 - July 31 2010
must bank by March 31 2010
February UY is probably best : It gives you most time to banking deadline & end of UY if you needed to cancel. It works for trips in April or summer months too because in event you have a trip planned for August and needed to cancel :
you would still have until Sept 30 to bank those points into upcoming UY if
you cancelled that August reservation 31 day or more before Check-In
OR if you cancelled that August reservation from 1 day - 30 days before
Check-In you wouldn't be able to bank those points because they'd go
into Holding status but at least you would have until January 31 to
utilize them.
You probably wouldn't want March UY because although those points are available until Feb 28 that wouldn't work well for a trip in February because if you had to last minute cancel February trip you are already past the banking deadline(Oct 31 2009) and you would only have to February 28 2010 to utilize those points.
Same thing for April UY - not enough wiggle room imho for a Feb trip concerning banking deadline & end of UY.
June could work for Feb, Apr & summer trips;
for a February trip you'd have until Jan 31 to bank, using dates above
if you cancel Feb trip 31 days or more before check-in ie your reservation is to begin on Feb 28 2010 but you cancel by Jan 28 2010 you could still bank those points because your banking deadline is Jan 31 2010
OR if you cancelled under 31 days but at least day before check-in
(on Feb 27 2010) the points would go into Holding status but you would have until May 31 2010 to try to utilize them.