If you are only going to buy one drill then a reasonable brand, corded drill with hammer action is all you need. Theres a limit to the number of shelves anyone can put up in the one house. SDS drills are ace compared to a regular hammer action drill when it comes to drilling into tough walls, but useless for anything else, and you'll not find drill bits for them in the local corner shop. To be honest, with a decent quality masonary bit like those light blue coloured ones that bosch do I do most of my masonary drilling with a non-hammer cordless. Hate the sound of the hammer action, so I only use it if the job actually calls of it, and 90% of the time it doesn't. Its only in non-domestic buildings, drill into solid, rough concrete, drilling for sleeve anchors etc that my SDS drill ever gets taken out of its box.
If you can get a mains drill with variable speed – look for a dial on the trigger – then its versatile enough to do many of the jobs a cordless drill can do – drive screws etc. Not quite as elegantly,they aren't as well balanced as cordless drills so its a bit fatiguing, but it'll do it, and you are spending the money on the drill rather than the batteries.