I assume the OP is talking new trucks, so some thoughts:
- Any truck that meets the ratings will do fine towing. A 3/4 ton will tow nicely but with a loaded weight probably on the order of 7500lb it's likely not necessary.
- You probably don't need the different rear end as the newer transmissions have lots of gears, so they can mimic the towing rear end by selecting a slightly deeper gear ratio.
- Look at the ratings of the specific truck. 1/2 ton trucks can have wildly different towing and cargo ratings.
Big question is how much towing vs around town driving will you do? Assuming it's typical 80-95% not towing, go for the best MPG truck that meets the tow ratings.