Just my thoughts on this thread:
First off, I agree with everything that Angrysparrow has said regarding a sewn loop at each end. However, just suppose you did find yourself with a damaged sewn loop on one end of your strap, why not live life on the wild side & just tie a knotted loop at the other end? I don't think you'd get arrested for it. Sure, you may lose some strength in the strap compared to a sewn loop, but probably no more so than where the strap passes through a cinch buckle.
(As a little side-note: We all know that putting knots in rope can reduce it's strength by upto 50% or more, depending on the knot, but I'm not convinced that this is anywhere near as relevant for straps because of their configuration. A strap for hammocking purposes is only going to be about 1mm thick at most, so the difference between inner and outer radii - & hence the stresses - is going to be far less than for a similarly rated rope. Or do I have that all wrong?)
As for rings Vs cinch buckles: Again, as per Angrysparrow's comment, it's down to personal preference, but I prefer rings for 2 good reasons:
First, assuming the strength reduction is as relevant for straps as it is ropes, the rings will retain more strength in the straps due to the much greater radius of the metal that the strap will be wrapped around (compared to the little bar in the buckle.)
Second is versatility, suppose you find yourself with a lost or damaged strap and the only temporary replacement you can find is rope. The rings will still work as intended with rope or strap, but the buckles will only work as intended with a strap.
Just my thoughts.