Pools can be the best or worst thing to ever happen to your backyard. After wasting four years of my life in the business, I will give you the "Scoop"
First Note** where every you buy the pool, that will most likley be the only place that has parts or pieces for that pool, just keep that in mind when dealing with a "Al's parking lot of pools"
Round pools generally cost less, and are easier to maintain than Ovals of the same gallons. Water circulates better in round pools.
While D.E. filter are going to be the best filtration wise, the work required is a bit more on your end. The powder must be replaced in the tank approx once a week, and the powder contains crystal silica which it states clearly on the bag "This has been found to cause cancer, in lab animals"
Sand is a good choice, simple and it is more forgiving on the new pool owner. It doesn't require the effort that D.E. does. Sand will get changed at the most, once a year at the beginning of the season. The more sand a tank holds= the more dirt and debris it will hold. Translation if the tank holds 150lbs of sand you may have to "backwash" it once every week, as opposed to a filter that hold 250lbs that won't have to get cleaned for 2weeks.
The pump for a 24' will be most likely a 1-1/2 horse power, you won't need more than that due to the pool being round.*****Note with filters and pumps Find and stay with either HAYWARD or JACUZZI brand******
Chemicals can be painful, but getting a good mineral system can keep the pool clean without heavy chlorine usage.