Ease of towing an 8-ft wide trailer vs a 7-foot trailer

You will see a big difference in towing between the two. The smaller Casita, with its aerodynamic, rounded front and sides, along with smaller frontal area, will be much easier to tow.

Wind resistance and frontal air drag are the most important factors in towing, IMO.

Yes, the Casita will have smaller inside room, but if towing ease and towing fuel mileage are important to you, the Casita would be my choice.