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The refractor is going to give a larger FoV than the Promak, a much crisper image showing better detail (to a point) and a better corrected FoV. However, being an achromatic, you'll will get some blue/violet fringing on very bright objects...though you probably won't notice it visually. You can get filters which will reduce this effect. One thing to remember though, the larger the FoV, the smaller the image scale for any given magnification...all things else being equal (i.e. lens/mirror size etc). You'll notice this more obviously if and when you decide to take piccies through the scope. However, you can get around this as well (to a certain extent) using a barlow lens or powermate to effectively increase the focal length of the scope. Given the Promak 150 and the SW150/1200 are the same size, I'd go for the SW OTA. In a comparison of the SW and the bigger Promak, I'd still go for the SW as the promaks of this size (being close to the size of the SW) don't offer enough advantage over the SW to warrant their purchase...except that the Promak 180 wil have somewhat better light garthering capacity and hence see a bit deeper....not enough, though, to really worry you.
The only advantage of the promaks is their portability.
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