At one time or another I've tried almost all of the methods. The scotchgard is the one method I can't vouch for. Its on my list to try this year.
Of the stream side applied products I like the Loon Aquacel (sp) best. Once it hits your fingers it melts into a liquid that is easy to apply.
If you use flys with CDC (Cul De Canard) in them do not use a floatant. The feathers have Preen oil on them which is a natural floatant.
And if you use the little holders that hold the bottle upside down at all times you may have a leak that spews floatant over your vest/pack.