If you're going to be using it mainly for for Field Target, I'd go with a .177. (There's a 20 fpe limit for Field Target) If you want to do some Field Target, but also some longer range (50+ yards) groups and longer range plinking, I'd go with a .22.
Just to throw a wrench into your thinking. If you will be going for best are accuracy as the main reason you're shooting, you're probably going to end up selling the Maruader and getting something more accurate. Might want to just start with something more accurate, perhaps used, and skip that step. Used BSA or Air Arms or FX would be a great choice.