While I love hot coffee, I generally only enjoy fraps at starbucks. I dont have one single favorite, but the top flavors I have enjoyed are the following.
-Caramel Frap (for something sweet and less coffee flavor)
-Caramel Brulee Frap (seasonal, is sweet with caramel sugar sprinkled on top but has a stronger flavor than the plain caramel frap.
-Salted Caramel Mocha (something a local starbucks offered for awhile, on top they sprinkle sea salt i think, in any case, freaken amazing how the caramel mixes with the salt and that flavor is out of this world. Has a real strong caramel/mocha flavor with just the right about of coffee added in)
-Finally, the Java Chip with 2 extra shots of espresso. (While not the best flavored, this thing will keep you awake for days with the extra shots in it. This one has never failed to wake me up regardless of how tired/exhausted I am. Has a very strong coffee flavor with chocolate)