It seems to me that you’re faced with the choice between accepting this as a limitation of your mind (which I have trouble believing) and learning to use SU effectively. You can not, practically speaking, continue to nurture your fixed concepts about curves in the SU environment. It’s a basic mismatch. You’d be smart to accept SU on its own terms if you wish to become proficient. Propping up your preconceptions with plugins sounds like a poor learning strategy.

It’s not clear from your post whether you’re even aware that there are no actual curved lines in SU: circles, arcs, and curves are all made up of straight line segments. The idea of “bending,” therefore, doesn’t really even apply. You can control the number of segments in a curve, and accordingly can make a curve appear “smoother” by using more segments, but only at the expense of increasing the model file size and ultimately degrading model performance. Try to use the default number of segments–12 for an arc and 24 for a circle–until you’ve had a chance to observe the way they appear on the completed 3D objects, not just on the raw 2D curves.

If you take your time and use small arcs with tangent inferencing, you should be able to fit just about any curve with a reasonable degree of smoothness. Once you have fitted a curve using a series of arcs, you can go back and adjust the number of segments per arc using Entity Info to make the size of the segments close to uniform along the entire length of the curve. Consistent segment size contrinutes to the overall smoothness and regularity of completed 3D objects at least as much as an abnormally high segment count. There are a couple of bezier curve plugins, but you may find that you rarely need them, as has been my experience modeling a variety of curved and compound-curved objects.

This forum can help you best if you tell us what you’re trying accomplish rather how you wish to go about it. The more specific you are with the former, the more specific a respondent can be advising you on the latter.

-Gully