14 is a steep climb. I haven't been up it since the road repair a few years ago, but there was a nice long passing lane. The switchback turns are not as tight as they are on 143. After the switchbacks, there isn't much for passing on up to the 148 turnoff, and it will be hard to get your speed back up till you finish the climb. 148 is a pretty drive, but is a hilly and winding road.
143 is also steep near the top, but is a shorter climb. After you pass Brian Head you will climb some more.
Loaded heavy I would do 143 (Parowan). With a lighter trailer or just a truck/car I would take 14.
