Soluble tablet: mint flavoured ones also act as breath freshener while melting under the tongue
Sachet: acts just as fast as soluble tablet if you can keep the gel under the tongue a bit. The point is that it enters the blood stream faster and more efficiently there (haven't tried it with a hot drink, which would mean absorbing through the gut but the hot drink might speed it up a bit).
Vardenafil or its generic: the smallest of tablets, much tinier per dose than cialis or viagra or their generics. Most studies suggest it has fewest side effects.
However user reports (which I agree with) say viagra or its generics give you the most reliable woody (necessary for ugly-attitude EEs or multiple shots). Cialis and its generics is handy as it gives you a whole weekend to allow for prossies fannying about and changing appointments.
Enjoy