Wes is spot on - fit and comfort in leathers is all that matters.
I have always done leathers (I dont have any textiles in my wardrobe - and I never have)
Go try some on. They are like boots / shoes - some will fit your body and others just wont.
I have tried the following - Richa, RST, Alpinestars, Arlen Ness and Dainese.
For my body shape and sizes Arlen Ness are the best fit - but you may find that RST leathers fit your shape better.
It just a case of trying some and going with comfort.
If you go for a mid range set you won't find too much difference in quality i.e. Double stitched and Triple stiched in stress areas - Kevlar stiching, crash protection e.t.c.
Comfort and fit is everything.
When you put them on they should be tight because they will soften and stretch with use (so tight is good)
- but they must be comfortable to wear. With a two piece suit fit is important (with a one piece suit it is even more important)
And sizing on all manufacturers is different - thats why you must try before you buy.
P.S. If you buy a one piece that's nice & tight "don't eat all the pies" as you will have problems getting into it and it's a very expensive exchange jobby :-)
