The answer is usually "what I am towing is the best." Best for them, but maybe not for you.
1. The toad should meet your transportation needs when RVing. It is real nice if the toad can meet your transportation needs otherwise. You need to consider how many people you want to carry, what other kind of stuff you want to carry, and whether or not you have off-road traveling needs.
2. For towing, smaller is better. Particularly for a gasser that might have a limited tow rating (a lot of smaller Workhorse chassis were arbitrarily limited to 3500 pounds).
I've had two.
I used a regular-cab manual transmission Ford Ranger for six years. I bought it at three years old, used it for hauling stuff to maintain rental houses when I wasn't towing it, hauling stuff to and from camp when towing it, and I needed to carry only two people.
When my wife died and I gave the family car to one of my children, I bought a Honda Fit and outfitted it for towing. It met my day to day transportation needs, could carry the occasional extra 2-4 people, yet I kept the Ranger for hauling stuff. I found that I was making my long distance trips in the truck because I found the Fit to be kind of buzzy after 10-15 hours running 60-80 MPH, and my back prefers to sit in a high seat, rather than legs stretched out in front. Keep that in mind when considering subcompacts and compact sedans.
When I started contracting out the house maintenance tasks, I traded the Ranger on a full-size 12 passenger van, which I converted to 8-passenger, because I had started traveling with kids and grandkids and the numbers added up to something bigger than 2 or 4. The Fit hangs in there as my towed vehicle, and around-town runabout.
All kinds of things work: Certain Jeeps, particularly the real off-road models, as Jeep is now just a brand put on a lot of different Fiat-Chrysler vehicles; until recently, Honda CRV and Fit; most GM compacts and subcompacts going back a long ways, some Ford compacts more recently; some GM and Ford compact to mid-size SUVs, Ford more recently than GM, although many of these SUVs are on the heavy side of Workhorse towing limits. There are a whole bunch of Saturn models, over the years, but really you are just talking about another GM brand, mechanically similar at first, badge engineering later.
A particularly popular 4x4 towed vehicle, not made for a long time, is the GEO/Chevrolet Tracker, and the rarer Suzuki branded models. This one is so popular that it is hard to find and carries quite high asking prices for a rather old subcompact utility even with quite high mileage.
If you need to carry more than five people, or more than four comfortably, finding something to tow four down gets harder. Finding something small and light that carries 6-7 people even harder, coming down to Suzuki's XL-7 Grand Vitara for a few years, and the Mazda MPV or Mazda 5, if you can find that one with a manual transmission.
Then there is the manual transmission option. Not all manual transmission vehicles tow well four down, but the choice opens up a lot of possibilities: Toyota, Nissan, Hyundai, Kia, Subaru etc subcompacts and compacts (even Pontiac Vibe if you can find it manual), and the current Honda Fit. But check carefully, there are manual transmission trucks and cars, even some front drive models, that do not lubricate properly while being flat towed.