If the two brands you are looking at are very similar, I would go with the company that you know does good work. Is you sister happy with her new windows and the job the company did? If so maybe think about those windows. If the bay window doesn't look right to you, try looking at their bow windows. They don't have steep angles like a bay. That means that there would be less vinyl between the glass areas. A little less sill area but they're just as nice in a big openening. Good luck to you.