transits are definately more supportive. i had the sphynx and when i went to the transits this year i felt a much more tighter fit around the toes and heel. so i would say the transits are probably better for a narrower foot.
...and there are PLENTY of them out there. They are known as "narrow" boots. At my shop, of all the remaining 2005 LF pro-model boots, about 70% were narrows.