After using a pressure filter for 4 months I would have to say that I would go with a gravitational filter. The issue is maintenance. With a pressure filter, you have to open it carefully, and scoop out all the water with a large cup/bowl in order to clean it properly. Remember the pressure filter is in the ground so this is on your hands and knees. Also, getting all the "muck water" out involves gloved hands. With a gravitational filter, the water is drained so all one needs do is open the filter and start cleaning the sponges.
Also, I have found that when the filter is not cleaned often enough, it gets clogged and slows the water flow down. At some point the filter may be so clogged as to stop completely; now think what this is doing to your pump. With a gravitational filter, if the filter becomes clogged - the water will just overflow and leave the filter. You might lose water but you won't lose a pump. So a good idea would be to make sure the overflow of the gravitational filter flows back to the pond and not into the back yard.
I intend to build my own gravitational filter next summer to complement the pressure one I have now.