I wouldnt buy an Alpha 170 right now. They are having issues with a few of them. They are working on a redesign of the impeller for the pump right now. They arent sure if the new impellers will be sent to just those having problems (pump surging) or to all 170 owners. The new impeller hasnt been tested thoroughly yet either. Basically, that is a lot of pump for the body of the 170 and they restricted it in part by the impeller design. There are reportedly only a few 170's having the pump issues out of the hundreds that have been sold. But I think they missed a bit on the impeller design on that model so the remedy is in the works. But I personally wouldnt be comfortable buying one until they straighten it out but it does look like the impeller is the fix. Im betting that the new impellers are fitted on subsequent runs of the skimmers and I would be waiting for that before I bought a 170. But just my opinions.
That said, I would NOT buy an Alpha 170 for a 180 gallon tank anyway. I personally would be looking at the 200.
I use an Alpha 200 on a 90 with 38 gallon sump ... light bioload. Larger tank in the future plan. The 200 has been an excellent performer and in restrosepect I would not hesitate to buy it again.
Premium aquatics forum has the Alpha skimmer club thread.
The MSX/SWC's with Askoll pump are great as well. I used one of the SWC sicce cones and swapped pump out to an askoll.
Personally, I would stay clear of the sicce pumps on the MSX/SWC skimmers. The pump can be finicky. The skimmers dont have the build quality of the Alpha skimmers or other RE made skimmers but they work great.
Warner marine and ATB get good reviews as well. The Sicce pumps work fine on those skimmers as they have been modified and are reportedly quiet. I considered the Warner cone as well but opted for the Alpha 200 for several reasons, the Askoll based pump being one of them.
Personally, I am a huge fan of the Laguna/Askoll based pumps.
Hear only good things about the I-techs too.
Lot's of good choices out there. I would find the respective skimmer club threads of the brands you are most interested in and read through them all.