http://www.Jehmco.com

it really depends on you.

But since it just for a water fall it really doesnt matter as long as it get the water on top

Nobody ever complains that their pump is too big – most people start out with something they think will be “adequate,” then realize it’s too small and upgrade within a year or two. So, I would recommend starting with something bigger than you think you need – almost all pumps have adjustable flow rates and if yours doesn’t, you can always add a restrictor for a lot less than a new, bigger pump would cost!

Laguna, Dynatec, Pondmaster, and Little Giant are all good brands; I like the Little Giant series, myself. As for a filter, I would recommend adding a veggie filter – an area of your pond that is densely planted with heavy-nitrogen absorbing plants like water iris and water hyacinth. As you pump your waste water into the veggie filter, the roots of the plants absorb the nitrates and let clean water flow back into the pond. Here are some links that illustrate the concept very well:
Http://www.Bonniesplants.com/how_to/veggiefilter.html
http://wernersponds.com/veggiefilter.html
http://frogpondphotography. Blogspot.com/2008/07/making-veggie-filter-for-my-goldfish.html

Hope this helps.