The trade-off between living space and carrying capacity on the one hand, and
MPG fuel savings on the other,
is an unavoidable one, very hard to get both IRL.
The latter would only become important to **me**, if I were planning on constantly driving all over the country, as in 20K miles per year.
The former is **very** important if you're doing more than weekend camping, or mind setting up a tent when staying a while.
And then look at reliability, a major third factor in your matrix. Can you fix it yourself?
For me, the up-front investment is irrelevant, it's per-year and **per-mile** running costs that are most critical, and fuel is but a minor part of that, especially for a cheap well-used vehicle.
Resale value may be important for some, fashion-status-appearance top priority for others.
Short answer, as others have pointed out is, "how long is a piece of string?"
It depends.