ammo supply local to you is pivotal if you don't reload, and if you would like one gun for roe/red that's comfortable to shoot yet has enough power, then look at 6.5x55, 25-06, 7-08, 260, 7x57, .270, .308, 30-06. Personally, if your local gun shop has a steady supply of quality ammo variations, I would opt for a 7mm (ie. 7x57). 6.5x55 can be a bi*ch to find ammo for, so can 7-08. .270 can to some seem overly heavy on the recoil front and 30-06 is maybe a tad overkill for a gun used primarily for roe, as is .308 IMHO. 25-06 and 260 are good calibres, again, sometimes (but not always) limited from ammo supply, and have limitations in how heavy you can go on the bullet front for big stags.
.243 would not be a bad choice at all, but whilst works fine, is on the marginal side of things from a red deer perspective..that said, I've taken more reds with .243 than any other calibre, and the .243 is simply a phenomenal roe deer round. There are also tons for sale in the 2nd hand market.
You also need to consider the gun itself, will you be buying new and having plenty of choice, or will you be picking something up used..if used then don't go for something which is hard on barrel life as you could easily risk buying something which needs expensive remedial work. Also ensure if buying 2nd hand that you pick a calibre in which there is plenty of choice in the market, so have a look at guntrader and gunstar and look at your budget range and what's available in decent guns that again, match with the ammo availability in your local shop(s), and which is neither marginal nor overkill...
if buying new, I woud go for a 7x57 in a classic configutation, without hesitation if your local shop carries good ammo, but there's few of them in the 2nd hand market as people who own them love them and don't let go of them.
Whatever you do, don't get caught up in magnumtitis and buy a cannon for a roe gun!!! ammo, budget for gun, availability, desire for comfort in the rifle (design and recoil0, all very important..any calibre will kill roe cleanly and swiftly with the right ammunition choice, so in essence, apart from recoil considerations, 'that' should be the last deciding factor in your equation..