Hi,
Im currently using 2 Eheim 2128s on my 500 litre tank, they run silently, rarely need cleaning if, like previously mentioned you use a sponge on the intake, are reliable and the fact that they heat the water aswell is great as it one less item in the tank. Priming these may not be the best system out there but once you have done it a couple of times and worked out which is the best way to do it its fine. As for cost, if you search around the prices have come down alot here in england over the last few years and theres some good deals on them.
On my smaller tanks, upto about 200 litres i use the Eheim ECCOs and the priming system on those is brilliant, again they are also silent and reliable.
I also use a variety of media and it doesnt have any effect on their performance.
I wouldnt use anything else. This is just my own opinion from my experiences over the last 15 years or so.
Regards
Dan