Your lens should be marked as "Normal" in Hugin, and the focal length multiplier of your camera is 1.0.
The auto-alignment in Hugin can be frustrating at times. I have found that the wider the field of view the more difficult it is for Hugin to align images. There are also a few different algorithms that you can choose to automatically select and align control points. The best one (by far!) is called autopano-sift-c. This algorithm is not part of the official Hugin installer (due to a legal issue related to patents). You have to install it yourself. If you are not using autopano-sift-c then you should give it a try. But even with autopano-sift-c, in pretty much every panorama I do I have to add more control points over the ones that Hugin finds on its own to improve the stitching.
Using the optimizer also requires some practice, since it has a lot of options. I typically start with a rough alignment of just orientation, then incrementally add more variables as needed. I use the "Custom" option a lot, to only optimize for the pictures that have problems, leaving the ones that are okay alone.
I've got decent results with autopano-sift-c using any "Normal" lenses, I believe the widest one I've used is 17mm. I have not had any luck at all using full frame and circular fisheye lenses though, for those I always select my control points manually.