I want to buy a kettlebell, but don't know what weight I should get.
If you don't have a gym membership, get a day pass and have a session with the kettlebells and whichever fits your need is the one to get.
Or, you can go to the store and just mess around with them Sport Authority & Modells in NY has a bunch of their weights on display, during the summer when I was younger I'd use to go in there and curl the 50s for 3 sets and leave. Needed a pump