I have used points many times and can't say I really understand what you are seeing. Generally if you enter the city on the find and reserve screen, check the box for a points reservation it will then give you a list of properties. You can sort by distance from the location, "cost" in points etc to select a property.

The "cost" will vary based on the property and reward availability, points savers are typically the cheapest and lower category hotels are of course less points.

This link gives you standard points cost by hotel category, I don't think there is a direct relationship between brand and category as their are other factors that determine this. For example I stayed in a Renaissance which I'd have expected to be a Cat 6 which turned out to be a Cat 4, apparently because property/land in the area is cheaper than many locations.

Bascally do your search and find a property that meets your needs based on cost, location and quality. If you are having trouble it may help to post where you are searching so others can try to observe the behavior you are seeing and advise accordingly.

Chris.