There are at least three operators of boats that will take you to Blaskett Island. You can leave from Dunquin, Ventry, or the Dingle pier. The total trip time is pretty similar but the time on the boat (versus time driving), options for amount of time on the island, and cost favors Dunquin, especially if conditions are rough. We'll be there in late May and will be out and about in the car anyway to visit Riasc and Eask. Any experiences to help differentiate between the choices?
Haven't made the trip over to the island ourselves, but we did spend time at the pier at Dunquin on our last trip. It's a very picturesque spot in its own right - you'll see several Currachs hauled out on the beach at the bottom of the walkway. Add the fact that it will be a much shorter journey over to the island and I think that makes it the preferred way to go if you'll be driving around anyway.