I've made lots of hammocks, so I'll chime in here. The ultimate goal for me is to be able to lay flat. The two best designs that I've seen for accomplishing this is the bridge hammock and the asymmetrical design. I feel too cramped in a bridge hammock, so I like the asym.
Really, the absolute most key thing (in my experience) is getting the gathering right at the ends. I start with a large rectangle (longer than you'd think), mark the tie out points (asym), gather the ends (you can optionally sew the two edges of the ends together here for several inches), place a length of cord in the middle of the gather at each end for the ridgeline tie out points, and then whip the ends together.
As for the gathering, some people like to just halfhazzardly collect all the fabric and whip it together. I like to make very meticulous folds (each successive fold bringing the outside edges to the center point). If your gather is off, you'll end up with really awkward tension lines.
I like to make the ridgeline adjustable so I can set the amount of sag I want on the fly. I do this with a taughtline hitch.
But now for the ultimate secret! On my asym hammocks I put pockets for a spreader bar (for which is use my trekking poles). This makes the hammock way more livable, and reduces any of those awkward tension lines you might have from construction.
Here are some pictures:
I know that's a lot of vague information, but I hope it helps.