Neither Poncha Pass nor La Veta Pass have the extended downhill like I-17 south of Flagstaff. That 20 mile drop down to Camp Verde is amazingly long.
I wouldn't worry about climbing either of those passes as both have quite gentle approaches all the way to the summit.
I would personally use Poncha Pass. One advantage it has over La Veta Pass is that the speed limit on the downhill side is 50 mph compared to 65 on La Veta Pass. It's easier to hold speed when you're starting from a lower speed to begin with. Once you're past Salida, the road in the canyon also has a lot of sections with lower speeds (50 mph) so much easier on your vehicle.
Thom's advises to use CO 115 does cut off the mileage through Pueblo but do be ready for a lot of traffic on CO 115 through Colorado Springs as you approach I-25. It does save quite a bit of mileage and interstate driving. Do make sure you're in the left lane as you approach I-25.
Try not to be on I-25 between Colorado Springs and Denver at rush hour. Amazing how many people communte between these two areas every day.
