No perfect answer here.
If you face a vapo with hidropump, solar beam is better
If it is an acuatail or worse a hydropulse you need a shorter duration attack to be able to dodge.
If not you can be hit after your solar beam cooldown and depending the CP difference you can be killed
Most of the defending vapos I see are acuatail or hydropulse so I´d go for leafblade
