This is a pretty wide open question. There are a lot of variables to take into account, so it's really impossible to say what tow vehicle is 'ideal' without knowing which trailer you're going to pull. Almost every feature can be a trade-off. A larger engine with more torque will pull much better going up hills and accelerate quicker but will typically use more gas. On the other hand some smaller engines may have to work harder pulling up hills and have to use lower gears which can sometimes result in worse mileage as well and shorter engine life.
The best answer is really a tow vehicle that has the proper ratings for specific trailer you want to tow. Once you know the trailers tongue weight, and fully loaded weight you can start to do the math to determine which tow vehicles will fit the bill for that particular rig.
Here's a site that can give you some good info to get started;
http://changingears.com/index.shtml
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