I will "third" the vote for Starwood. Not only you get the hotels, but if you do want the miles (if you travel to destinations like South America or Asia where hotels are cheap and flights are expensive, miles may be a priority) you have the pick of the litter of the airlines aside from UA (due to bad conversion rate). That way, you can call each airline one by one and find the one that has the award available.

The starpoints are the most valuable once you have them, but they are probably the hardest to come by, not nearly as many opportunities to earn them and the amount you earn per $ spent (on hotel/airline) is usually less than what you would get with airline miles. That is probably why they have been able to maintain a higher value.