Check out something with a higher voltage over something cute. The higher voltage in itself doesn't really do anything, but it means that the battery pack has more actual cells in it. This means that it has more 'grunt' in it under load and it doesn't have to work as hard when you push it. This means that the battery packs (the most expensive part) will last longer.
Make sure you know how to treat your battery packs. Check the website and ignore what the salesman says. If he's just a warehouse depot or general hardware type clerk, he probably doesn't know *&^* about batteries and current battery technology.
What I did when I was contemplating the same thing was to look for a guy who REPAIRED and worked on INDUSTRIAL/Professional use tools.
I found a Japanese made cordless drill rebranded for direct sale that had Japanese made Panasonic batteries in the battery packs. I bought one extra battery pack and the whole thing cost me about 90 dollars US. The Batteries are actually 12V, as opposed to some of the higher voltage offerings at the local hardware store, and I would have preferred a higher voltage, but it was the only one that had Japanese made batteries (the guy replaced them himself - and showed me inside)...
However, you are not likely to have this decision to make. Amongst the Chinese made offerings, go for the highest voltage available. In a hardware store, everything will be made in China. Period.
Amongst cordless drills, there are three main types.
Hammer drills are for drilling into concrete. The drill bit usually runs about 1500 RPM (this is pretty slow compared to a corded drill) for this and moves in and out like a hammer. Hammer drills are often dual-purpose with clutched drills for screws. Hammer drills often have faster rotation speeds, but sometimes you can only get this rotation speed with the hammer, in-out, motion.
Impact drills are specific purpose. These are generally for loosening stuck bolts. The listed torque is MUCH higher than a standard drill, but once it passes a certain limit, it won't just twist, it will actually use an air-drill-like mechanism to smash repeatedly in a twisting motion. I have this type. It is much more resistant to burning out the windings since it has a specific set reaction to getting stuck. BUT it's not very good for putting screws in since it will chew up the head and use the screw to tear up any wood you might be drilling into if you are not careful. It's only recommended for a more experienced and careful user. RPM is around 3000 which is about the same as a standard corded drill.
Clutched drills are specifically for screws. They are sometimes called 'screw guns'. They have a mechanism for getting stuck as well. When the resistance gets to a certain point (you can set this with an adjuster dial at the end), the clutch slips and the motor keeps moving. This is good because it doesn't keep trying to turn the screw, preventing damage to the screw head, and preventing overtightening/stripping the thing you are drilling into. It also prevents damage to the electric motor which gets damaged when it gets stuck (sometimes just a little bit at a time, but it adds up). These are usually pretty slow too. 500-900 RPM with 700 or 750RPM as an average. For a guy like me, this is painfully slow. It's not really very suitable for drilling holes either if you ask me.
Another thing to consider is the battery type. Find out how you need to store it. A lot of people buy cordless, use it for a few days, then store it for a couple of years, then try to use it again to find that the battery can no longer hold a charge. This problem has been addressed by SOME battery manufacturers in the last year or two, but that tech has not yet filtered down to every type of drill, so this can still happen.
Honestly, cordless drills are convenient, but are best suited to those who use them frequently. If it's something that you use at least once every three months, that should do it.
If not, you might want to consider a corded drill and a light extension cord.
cheaper initial cost
no batteries to muck about with
USUALLY stronger electric motor
Faster rotation speed
USUALLY a better ability to adjust the speed with the trigger
You can add stuff to the end to meet specific needs (a clutch can be purchased for about 15 bucks and can be installed/uninstalled fairly easily).
Yes, I have a cordless drill, but I also am in the habit of buying scooters/motorcycles and tearing them down to bare skeletons on the spot and visiting junkyards to scrounge parts... being in and out of a junkyard quickly has a surprising effect on the price you end up paying for stuff - they think you got less, they think you are more 'pro'... I've seen prices as low as 1/4 of what I expected for parts just because they see me as a mechanic when really i'm just a tinkerer.
Regarding the ends, there are two general types.
The quick-release, 6-sided type
The chuck-key and three-fingered clamp type
if you just do screws, the quick release is fine. You can even get a few smaller drill bits with this type of attachment. It's very convenient.
However, if you want do drill anything with precision. If you want it to deliver consistent torque that is straight, you are generally better off with the clamp type. Any sort of drilling or grinding would fit the bill here.
Brands like Ryobi and Black and Decker are common in hardware stores and are generally 1-2 year disposable tools. Bosch is usually worth the few extra dollars. Miyako (actually, I think I spelled it wrong, sorry) is another good brand.
Be aware of newer 'chinese' branded stuff. If they are using more modern technology, they might actually be BETTER than a US brand like Black and Decker. This is because most US hardware store brands switched to China a long time ago, but might be behind on the tech. This is sometimes true with the pro/industrial grade stuff too.
Hope it's helpful!