rabbits 22lr
fox only .22-250 or .223
fox and roe .243 or anything north of here really. If you want the option of adding in sika, fallow or reds, you should really consider .260, .270, 6.5x55, 7mm, 7-08, .308 as well
Personally - I use a .243 for fox, roe, and red calves. .22LR for rabbits and rook branchers, and .308 for red stags and hinds. 6.5x55 and 30-06 as backup, but they're just collecting dust really.
to be honest, you can get into 'which rifle' debates from here to eternity, and everyone will have their favourites and opinions, but at the end of the day they will ALL work. so the best advice will be to consider what you'll shoot and how flexible a range of species you want your weapon of choice to accomodate, and then pick a good quality peice of equipment that's within your budget range, and which allows you to put some good optics on as well. Ideally it should be easy to get ammo for that calibre, and it should be something that not only catches your eye and inspires confidence, but which fits you well and that you will grow old with. unless you'll be doing a lot of sika/red stag stalking, a good .243 such as a sako will do you great for the rest of your life I'm sure.