Here is a site I ran across on a rod building forum, which is a system for measuring a fly rods action, stiffness etc. There is data for a lot of common rods and blanks, although nothing really recent. It is the Common Cents System and the rod data. It is a pretty clever system in that anybody can measure any rod with a tape measure, a paperclip, small baggie, and pennies (for weight - you should have 50 cents or so of pennies). You also need a level and a protractor to measure the angle of the rod tip. Some manufactures of rod blanks list the CC data for their rods, too bad more major manufactures don't. - Anyway, it is interesting to look at some measurements.
I would suggest there are a number of things to consider in fly rod choice, imho:
What size flies are you going to be casting? (small dry flies, shallow water = 4 wt., large weighted wooly buggers on a sink tip line = 7wt - you get the idea, smallmouth or small trout? Where would you be fishing most?, which leads us to the second consideration.
How deep of water ? small shallow mountain lake in a float tube, or bigger lake, bigger boat? Shallow water argues for lower line weights (to avoid spooking fish), Deeper water usually means bigger flies, bigger fish, higher line weight. In general, higher line weights are easier to cast a long ways, although for myself (and I suspect a few others), it is safe to assume that distance is limited by my skill, not my equipment. Good casters can throw a bamboo 4wt farther than I can my latest generation graphite 7wt. I have heard some folks in float tubes like longer rods (like 10'), since you are kinda low in the water, but I haven't tried it.
Then there is casting - what is your natural style? If you're the quick, nervous overachiever, by all means get a fast action rod - it will suit you. If you are the mellow Tai-Chi sort of fellow, get a moderate action rod. If your the crafty sort, it's not difficult to buy a kit of parts and wrap your own - its fun, and even a beginner can make a rod to rival the top name rod manufactures, for well less than 1/2 the price. [down to a point, very inexpensive rods you are not going to be able to buy the parts and pieces for less] Then after you take up fly tying you can catch a fish, with a rod you made, on a fly you tied - which is pretty cool.
All this to say there is no best rod out there - only what would you enjoy casting and fishing on the waters you plan to fish with it, for some that would be a 10', 7wt graphite, for other's the four weight bamboo. (which, incidently, is off the slow chart compared to the graphite, but for which folks are willing to pay thousands of dollars). It's not a competition, fast is not better than slow, stiff better than sensitive, etc. If its your first fly rod, a six weight is a good average.
Michael