The best is Kamagra Gel in small sachets, even comes in 4 flavours and works faster than the tablets with no side effects, however I only pay 80 to 100baht per sachet in Patts and Bkk so Phuket seems expensive to me.
Cialis or its cheaper generic also works well and lasts longer with no side effects for me either, I usually pay 400baht for 4 tabs although there is also a gel version out now at the same price, 100baht per sachet - these prices are Patts though.
Personally I dont take either all the time as I'm still reasonably good without, however we all need the occassional hit now and then especially if you indulge 3 or 4 times a day ......5555 - or like me 1 or 2 times every other day ......55555 (mind you it is with the same girl)