It helps a LOT to sit down and decide what you intend to do with it. There is a huge difference between a big one and a little one.
Here in the UK, most houses are built from brick. Brick varies hugely with location and local geology. Around me, the geology means that most brick is made from shale and is ****** hard (the Empire State Building was built on "Accrington Nori" brick foundations, shipped over from England, because it was one of the few bricks hard enough to take the weight of the structure without crushing. Accrington is about 8 miles from me). Drilling brick walls with an overly powerful SDS tends to knock the back out of the bricks. The same thing applies to concrete block walls, though to a lesser extent.
Here, I'd recommend the cheapest 2 kg-class (circa 2J impact energy) SDS you can find as an ideal DIY drill. If you are already into an 18V battery system, an SDS from the appropriate range would also be a good option. Expect to be able to drill up to 1/2" holes in brick/concrete/masonry with no problem at all. Up to 3/4" will be doable, but will be noticeably slower. Occasional holes up to 1" will be achievable, but not something you'll want to do often, in my experience.
Clearly the construction methods in your location will affect the tool most appropriate for your use. If you anticipate needing more grunt, by all means get a bigger machine (3-4 kg and >3J impact energy), but expect it to be quite destructive if used for more delicate tasks.
I have used a range of SDS drill bits at different prices. I do tend to buy from drill suppliers, so have probably been spared dealing with the really cheap ones that just don't work. My experience is that the "good" ones last maybe twice as long but cost 3 times as much. Sharp is a bit of a misnomer with SDS drill bits, but "sharper" ones drill much faster than blunter ones. Cheap carbide doesn't seem to wear much faster than expensive Carbide. Buying cheap and changing often will get more work done in any given amount of time than buying expensive and trying to eke out maximum use from an expensive drill bit, in my experience.
