I've read that others in these forums like the Penguin 350 a lot also. I have several Emperor 400's & 280's as well as the Penguin 350's, 170's & 125's. The spray bars are an issue I suppose, although I've had very infrequent troubles with mine, but IMO the benefits over the Penguins and others are worth it.
The Emperor has the largest well of any H.O.B. type that I have (also have numerous Tetras, Aquaclears & Whispers), so the extra water volume is a plus. Additionally there's room for the filter cartridge, a media cartridge and more. I've had very good results with the Seachem Purigen polymer in other filters so now I'm going to add a bag of it in after the media cage in my 400's - can't fit all of that in my Penguins, Whispers or Tetras. Aquaclears are a little different.
Then there's the biowheel. I understand the function / design but I have now way to clinically evaluate its effectiveness. Anecdotally I can say that I have them on my most challenging tanks (18" & 10" plecos and 12" channel cat) and they do great as long as I keep the cartridges from clogging, and that does happen fast with these guys.
Overall I'd buy another if I had need of any more HOB filters. I've gotten some really good deals on used ones, just make sure that all of the parts are there and include the cost of a new impeller and probably bearings just in case, before you make an offer. The bio wheels last pretty much forever as long as you don't damage them.
Just like anything else though. They all seem to work well as long as you do your part. Most people fall into the trap of thinking that a more efficient filter means less frequent attention, water changes, etc.
I've gotten good deals from ebay, Big Als, and on these filters in particular, from Ken's - around $48, and they both ship pretty quick. Al's won't match Ken's prices though when he is cheaper.