I did some research not too long ago, so here's my input:
Each manufacturer has it's own criteria,
Spidi split its line of clothing to sport, naked, custom & enduro. The sport line is tight fitting naked is loose. Leathers that'll fit both categories are somewhere in the middle.
Alpinestars tell you in a 7 grade level how the fit is between relaxed & fitted, the sleeve profile between straight & 90 degrees curve, the ventilation low to high and water resistance 0% - 100%.
Each manufacturer has it's own parameters.
Avoid buying without trying on first, or at least make sure you can send the leathers back if you don't like the fit or to change to a different size.
Best companies in my opinion are: Spidi, Dainese, Axo, Alpinestars, Arlen Ness, Berik and Spyke. (I think Berik is sold in the USA in limited form under the brand name MOTOGP, the logo looks identical).
A 2-piece suit is a good idea, you can mix sizes for top & bottom pieces.
I bought a Teknic Silverstone one-piece as a leftover for 290 bucks... It was a deal and I like the suit for the price. However, it doesn't fit as well as a custom suit and if I had to do it all over again, I'd spend the extra cash and look into Syed leathers (which seem to be the bargain in custom suits). Check them out:
I wanted to pick up a pair of perforated leathers for summer riding. I tried on everything I could find, Vanson, Bates, Dainsee, Motogp, Joe Rocket etc... I ended up running into a gentleman named Mansoor, owner of Road Gear, at the international motorcycle show. He had me try on the XKJ Jacket and I was sold. I recently purchased the XKJ pants also. They come with full liners that I have been using for 45-65 degree riding. The armor is well placed and comfortable. They will send you 2 sizes if you are unsure, but then, they do have your credit card at that point. Pull out the liners and it better be fairly warm cause these things flow air everywhere.
Downside- No zip together option for the pant and jacket.
Although they fit me perfect off the rack, custom made is custom made and you can't go too far wrong with any of the brands mentioned above.
I bought the jacket at the show for $300 (normaly $498) and ordered the pants over the phone for $300. Not a bad deal when you start adding up armor and liners.
Kangaroo hide is much more comfortable to wear. It is hard to find in the U.S. though.
Frank Thomas just came out with a Kangaroo hide (both in one- and two-piece) suit for only $900. Frank Thomas also has a little more room in the torso (it is an English brand, versus the skinny italian cuts of Alpinestars and Dainese). If you have a gut, these'll work. If you have more than a gut, well, lose some weight and use a new set of leathers as a motivating factor.
You'd be hard pressed to find another kangaroo hide for that price. Frank Thomas is sold at Cycle Gear.
Check out MO's product section, there's an article about Syed Leathers: $875 for a one-piece set of custom-tailored leathers. For a bit more you can design you own suit and make it as hidious as you like.
You can probably go to a shoe-repair shop and have a zipper installed to connect your 2 piece. I replaced the nylon zippers in my Sidi boots, with brass, for $20. So I figure you could probably do a wrap-around suit zipper for about $50-60, depending on where you live.
Vanson Leathers off the rack stuff is a lot looser than Italian and other Euro made stuff. While not the most trendy styling it is made to last forever. Trendy leathers go out of style pretty fast. A two piece system is the way to go for the street.
I have been trying to find info on genuine Kangaroo for a while now too. To my dismay Alpinestars doesn't even offer a real kangaroo suit.
So far this is what I've been able to find:
Teknic's top-shelf suit, the Speedstar, is Kangaroo. The top of the line MotoGP-branded suit is also supposed to be Kangaroo, and Spidi offered a Kangaroo version of it's top-level suit at one time, but I can't seem to find anyone offering one from them now. Lastly, Dainese seems to have a kangaroo version of their T-Bora suit (I think that's what "canguro" means, $2649 at Kneedraggers, but you better trim and lean if you're buying this suit.)
You can expect to pay at least $1500 for a real kangaroo suit.