Howdy,
If you are going to be towing a single bike on a small trailer, then a car will probably work fine provided it is not a little car. The biggest problem with cars is that the suspension is so mushy that any tongue weight on the trailer will make the front of the car stick up and the steering will get wobbly feeling. Take our saturn for instance, I think it would have the power to pull and stop a trailer with a single bike without too much trouble. But it would have to be one of those little frame trailers that aren't much use for anything other than towing a bike.
I would go for a small truck in your case. I know you don't want the ground pounding fire breathing monster truck like my Dad's because you will never be pulling a huge trailer loaded with bikes like I might. A truck like Will's might do okay, but his is hardly any better than a car because he got the smallest engine with the softest suspension. However, you could easily put either of your bikes in the back of his truck and strap them down. You'd have to leave the tailgate down though.
You've seen our two bike trailer right? I would not want to pull that trailer with Will's truck. The weight of the bike combined with the trailer would make the truck weave all over the place. Heaven forbid you pull the trailer anywhere that the terrain gets hilly. His truck would have a difficult and slow time of climbing any kind of steep grade with the trailer.
The dilemma is that if you get a small truck that gets good gas mileage, it won't have heavy enough suspension and enough power to pull a trailer. However, it will be fine with the bike in the bed. A small truck with enough power and heavy enough suspension really won't cost much less than a full sized truck and won't get much better mileage. Maintenance on a full sized American truck will likely be a little cheaper than on a foreign model. A used F-150 extended cab would be nice but don't expect more than 15-18 mpg. The little trucks might get better mileage when you are not towing, but as soon as you put a heavy load behind them, the mileage drops off real fast, often lower than a bigger truck.
Having towed many trailers with both large and small trucks, I personally prefer to have the towing vehicle as large as possible relative to the load being towed. Otherwise you get a bit of the tail wagging the dog effect. Not fun! Since you commute on the bike so much, I would be less concerned with daily mileage for a truck and focus more on how well it can handle a loaded trailer.
I'm still trying to convince my Dad to sell me his F-250 Turbo Diesel crew cab
You never even notice the trailer even with four large bikes on it. It gets about 15 mpg at 80mph pulling a big load. Power is never an issue
And it's real plush inside!