To be able to give you a proper answer, it would be helpful to have a bit more information such as:
1. Price range
2. New or used, or either
3. Actual plan for use. Do you want something that can be a rock crawler? Or something more suited for dirt roads? Or either?
4. Ideas on future build. Do you want to put a camper in the bed? Pull a trailer? Add armor? Lift it? Payload is something that not enough people consider, and can be a limiting factor with mid-size trucks
5. Any other "must haves" besides heated seats? (which all mid-size trucks offer)
High some VERY high level pros/cons for the mid-size trucks:
1. Tacoma
- Pros: Reliability (though I'd argue that a new Tacoma's reliability with the 3.5L isn't really any better than the Frontier with the 4.0L or probably the Gladiator with the 3.6L), aftermarket support, resale value
- Cons: Cost, Payload in off-road trims (1,100lbs-ish), seating position, low-torque engine once you begin to build out your Taco
2. Colorado/Canyon
- Pros: Diesel option, cost on used market, ZR2 or the Bison trims offer great off-road ability
- Cons: Aftermarket support, reliability, interior quality
3. Frontier
- Pros: Cost (either new or used), reliability, fully-boxed frame and Dana 44 rear, simple/durable interior
- Cons: Ancient interior, payload not much better than a Tacoma, no current safety tech
4. Gladiator
- Pros: Capability (even in Sport trim), resale value, aftermarket support, payload and towing, interior quality
- Cons: Cost, overall length
5. Ranger
- Pros: Towing and payload, fuel economy (at least on highway)
- Cons: Cost while new, 4cyl. may not be for everyone, unknown reliability, aftermarket support
Personally, I was in your shoes about 8 months ago. I decided on a lightly used, '16 Frontier Pro-4x for a few reasons: 1. Cost - you can get a brand new loaded Pro-4x for $30k, or you can follow my footsteps and get a lightly used model (which is the same exact truck...since they never change) for even less. I also really enjoyed the torque from the 4.0L engine as well as the responsiveness of the ancient 5-speed auto. I looked at Tacomas, but being 6'1" I did not enjoy the seating position, nor the outrageous prices they sell for out in Denver. I never drove a Colorado or Gladiator, but drove a new Ranger and while I liked it, I felt they were severely overpriced at the dealerships and I was unsure how well the 2.3L would hold up over time.
Ultimately the price and simple nature of the Frontier won me over, but YMMV.