As said already, the .22 rimmy is the rabbitting workhorse and should be a standard on any FAC application. Don't rule out the .17HMR, it has its uses so I would recommend asking for both from the outset. If you think you can get .223 on you first application (no reason why not) then don't bother with Hornet (my opinion lads don't get upset).
Really it's about what you need not what you want/can get. There is a tool for every occasion so work out what you want your rifles to do for you and then look at what fits the bill. Range, noise, cost, reload, expeience etc, all thing to take int