Maureen,
I have no experiece with either brand of pool, I'm partial to sand filters thats all I've owned and they have been super easy to take care of and do a fine job in my opinion. The house I'm in had a 18' round pool backfilled/dug in like you are thinking about, after having to remove it (pool shot) filling the hole and installing a new larger pool i personally wouldn't do it. What is going to become of the dirt you excivate, if I figured correctly depending on the pool you will have a minimum of 37+ cu. yards to disperse or get rid of. On the main drain, all i see is big hole in the lowest part of my liner and that is something that doesn't sound too good.

Getting the discussion started,
JJ