I have read for hours.. can someone talk me through this again?

We need to install a power pack inside a custom cabinet. Builder wants to know what we are buying so he can build the case around it. Only problem is I don't know what the heck to buy. 36" hood over a 30" stove. I know I need a power pack and a liner, right?

We went to an appliance store and they said our best choices are from xo http://www.ajmadison.com/cgi-bin/ajmadison/XOI27S.html, ($549)

Broan Elite RMP17004 ($549) http://www.sears.com/broan-27inch-built-in-vent-assembly-for-custom-cabinet/p-02258153000P?sid=IDx01192011x000001&gclid=CIjKkIKInsoCFYQfHwoduxQBRw, 

or Best Coperto ($936) http://www.bestrangehoods.com/store/products/catalog.aspx?key=93bdbaee-d312-4f5d-a5d4-973b0dc6a729

Besides the price difference is there any other differences between these I should consider? Thanks!