The things that you should take into account when choosing a filter are:
1. How much debris you get in your yard or pool. (Any overhanging trees, flowering trees nearby, lots of mulch or dirt that could potentially wash into the pool with heavy rain? Are you scooping up large amounts of debris off the pool surface daily? How much fine particulate debris is in the water? DE tends to filter the best, Cartridges filter as well or better according to some folks, Sand filtering can be improved with the addition of DE. All filter types give good water clarity.)
2. The characteristics of your fill water. (Fill water high in calcium, iron, or copper. Well water that takes a long time to provide adequate water for re-fills. Cost of water in your area. Any restrictions limiting the amount of water used per month, or restrictions on the discharge of water and where it may be discharged. Backwashing sand filters use more water, and if you have to backwash often you will be topping off your pool more frequently. If your fill water has metals that will require more frequent additions of sequesterant to prevent stains. If your fill water is high in calcium, frequent water additions will result in very high calcium levels in the pool which will require more diligence adjusting TA and pH levels to prevent scale formation. If water is rationed or expensive in your area you will want a filter that uses less water, generally cartridge systems use the least amount of water.)
3. The amount of time you can devote to filter maintenance. (All filters require a thorough cleaning at least once per year, more often if you don't keep the water balanced and develop algae, or you get a lot of debris in the pool. DE filter maintenance is very labor intensive when you need to clean the grids. Some DE filters are plumbed with a multi-port valve that allows you to backwash. Backwashing will remove some of the dirty DE, you will add fresh DE and continue filtering until backwashing no longer improves flow. Then the DE filter will need to be opened up, and the grids hosed off to restore optimal function. Some areas have restrictions on how used DE is disposed of. That would be something to look into if you are considering a DE filter. Cartridge filters are cleaned by removing the cartridge, hosing it off and putting it back. Cartridge filters typically use less water to clean.)
4. Cost. (You want the largest filter you can afford, regardless of type. Cartridge filters tend to be more expensive up front, and replacement cartridges may be expensive as well. DE filters require at least 1 change of DE per year. DE tends to run $25-30 for a 25 lb box. DE substitutes cost a little more. Sand filters require an initial installation of sand, but that same sand can be deep cleaned once per year and used indefinitely.)
It helps to make yourself a little chart so you can compare the pluses and minuses of each type of filter for your situation.
