[Richard]

I would suggest not to stress on name brand. All the manufacturers source the least expensive parts they can get to build their products, even the big names. You will find the same parts from different sources in the same unit depending on the manufacture run. Most failures in A/C products are due to installation. This is not so much a problem with window units as it is more or less like buying a fridge or other self contained appliance. All AC units still use the same technology from when it was first designed. More money usually just means more bells and whistles and better warranty. Every place I worked at since 1982 decided equipment to be sold based on profit margin and manufacturer support. If you are handy pop the unit apart. May be something as simple as a run capacitor.
Edit- Yes more capacity would not hurt. I am sure some may disagree but in my personal opinion 400-450 sq ft per ton (12,000 btu) is in the maintain category for a constantly conditioned and well insulated home. If you are interested in messing with the unit PM me and I will give you my cell.