PBs like cartridge filters because it limits the phone calls after the pool is built. They do a fine job.

I like sand filters and for a lot of years it was the only type of filter that I put in my builds. the reason I like sand filters is that when I get the call "my heater doesn't work" I can say when was the last time you cleaned your filter and after the traditional "I have to clean my filter?" I can walk them trough a back wash on the phone and they are always glad to have it fixed immediately without having to spend an hour hosing down the filter. they are easy to maintain and don't require that you have to have a bunch of D.E.around. they work best with a filter aid (like extreme clean or bright and clear type stuff) this is the way that pretty much all of out drinking water is filtered and they do a good job in a properly maintained pool. the cleanest water will come from a D.E. filter but they can be a bit of a pain to keep maintained too.

As Brent said, all of them will do a good job. DE will do the best filtering job and is between the other two types for maintenance. Cartridges are second best in filtering but require the most maintenance (though it's still pretty straightforward and not very time consuming). Sand is the least effective filter (though still very good and certainly good enough) but is the easiest to maintain. Using zeolite instead of sand in a sand filter will make it marginally more effective (probably approaches a cartridge in its filtering).

I'd be wary of the guy who's telling you sand is crap; he should be giving you the facts instead of trying to sway you to the technology that makes him happiest.

Whichever filter type you choose, it's good practice to oversize the filter. It will do a better job and won't need to be cleaned as often.

Thanks so much for the input. Do you waste a lot of water doing the back wash? I think that was one reason he said sand was bad. I really appreciate the advice. I never knew how many decisions there were to building a pool...very confusing at times! Any thing you would have done differently?

Sand filters have been the standard in swimming pools for 40 years+. Cartridge filters are three times as much money but filter three times smaller particulate from the water. Both require maintenance with the sand filter needed 10 minutes every 1-2 weeks and the cartridge filter needed 1/2 day every 6 months or so. The biggest question that you have not addressed in your post is which pump are you going to be using? When sizing a plumbing system the pool volume, pump flow rate and filter max GPM values must all be considered. Be aware that most pool builders just follow a general formula for the pools they build and do not actually run these calculations for the most part. You would be well advised to learn more about this subject so that you can make an informed decision for your filter - how to choose the right pool filter