I use Eyelash Emporium Ultra Platinum. It's good for classic and volume. It's a good price and last ages, you only need a tiny amount of adhesive for a good bond and I keep the bottles in tiny air-tight jars with dry rice in to prevent moisture affecting the shelf-life.
I've also heard great things about Sky glue (which you can buy on shop LadyLash, and buy a tester size to try) and Flirties whose products are all on BeautyTrix (I like their primer - and I also use protein remover pads on lashes before I do anything else).
But don't forget, the optimum adhesive for you depends on the temp and humidity of your working environment as well as your methods of working. X