The first thing you need to think about when buying a sump pump for the basement is the type of sump pump you need. There are basically two kinds. The first is called a pedestal sump pump which goes into the sump pump basin or the hole that you put into a hole that is put into the basement. Some of it is above the hole, therefore it can be tipped, it can be tied up with the cord. When you need it, it may not turn on.
The second type is submersible. These go fully into the sump pump basin, so you can't see it above the edge of the hole or basin. These are the most reliable because there is less chance of damaging it from above.
The next consideration is how powerful the sump pump is, how many gallons it pumps per minute, but what is even more important is how many gallons of water it pumps per minute at certain elevations. For instance, a sump pump is below the floor pumping and it is great that it can pump water out at a foot. But, it is more important to see how much water it will pump out at 10 feet because the pump is in the hole, there is a pipe that comes up out of the sump pump, and then there is a pipe that come up out of the sump pump and goes through your foundation at about 10 feet. So that is the measurement that you want.
Dependability is another factor that needs to be looked at. On a sump pump it is the switch. When you look at some sump pumps, you'll see there is an arm attached with a float on it which rises to turn it on. That arm can get tangled in cords or debris and is not too dependable. A better type of switch is a rod with a float on it which only goes up and down. As it rises, the pump gets turned on. This is much more reliable. Look for the sump pumps that DO NOT have an arm that goes up, but that have a rod that goes up and down.
Durability is also a key factor. Some sump pumps have been in use for over 30 years. These are cast iron. I'd look at sump pumps that have cast iron housing.
There are some other considerations. Some people look at the energy efficiency of sump pumps. This can be important to some people, but if you think about it, they only turn on when you need them. They have a small motor and don't use too much energy when in use. So this is not as important as the other factors.