Fishkeeping - I need a good water pump for my pond

I have a 9'x7' semi round pond that at one end is 16" deep and at the
other end is 20" deep, with a water fall at the deepest end. (I am
currently borrowing my friend sump pump (1/3 horse). I like it, but he
told me that these sump pumps from home depot tend to leak from time
to time. Oh yeah, he wants it back as soon as I buy my own. I also
have a home depot water filter which is in the water, which I don't
like) my pond is around 700 gallons. It is only about 2 months old.

I have order a kit from Skippy's to make a 100 gallons stock tank
filter that will be good for ponds up to 3500 gallons. I know that it
is an over kill but I am planning to expand the pond in the future. I
will be adding a second pond with a creek in between both. So I need
as much filtration as I can get, but I need a good pump to handle my
needs now and in the future.

I deviating between a water pump (Meg-drive) or sump pump (well type
that it is continuous use) or water fall pump. I have $225.00 dollars
to spend on a good pump. I would like something that is going to last
me for a while. I also know that sump pump may leak. I have also read
here, that Meg-drive pump may or may not last more that 2 years.

I am clueless and I need all of your folks help and suggestion on
this.

I know that some of you have been doing ponds for a long time and have
great suggestions for this rookie.

Thanks,
Carlos