Eheims are very nice reliable filters, but very pricey.
I've heard some bad things about the thermo-filters and the wet/drys though, some problems with the heaters and such. I would advise a standard model and regular heaters either in tank, inline or in sump.
For a lower $$$ the Penn Plax Cascades are supossed to be reliable and efficient, I will probably use this filter on my new tank.
But for a 180gal I'd like a nice wet/dry sump either by itself or working with a canister, if the wet/dry sump is large enough to just handle the system then the canister becomes the nice little extra filtration every tank needs and a emergency back-up.