DiD has come out with some of the best in all three of your categories of late, although Soldier Story has been coming out with some nice boxed figures. Dragon also makes very decent figures and are sold at a better price point. Mixing and matching isn't much of a problem when it comes to color of WW2 US uniforms, when you get to know more about those uniforms and the variation of dye lots you'll understand. Olive Drab, or O.D., is the standard US military combat uniform color (as it was for armor and other vehicles and for a time aircraft). O.D. could vary from green to brownish green to almost khaki after repeated washing and/or fading. So depending on your subject you've got some leeway, best to find photos (color is great) and well researched color illustrations, or photos of actual uniforms with some information about the color and use (where, when, who).
The fit of clothing really depends a lot on the body you choose, some manufacturers clothing fit better on some bodies and not on others. Poseability, height and sometimes bulk are what influences my choice of body. There are a lot of threads that you can peruse on OSW that discuss particular bodies. Personally I would be more concerned about accuracy of the uniform for the particular period you are representing (the same should be said for the accessories - weapons, etc.).
A WW2 US Airborne paratrooper is a good example, what he wore on D-Day would be different from his appearance subsequent to that battle. During the actions at Bastogne in the Battle of the Bulge for example, Airborne soldiers may been seen wearing the M1943 combat uniform or the M42 (with certain changes I've specified below). The M42 remained in use until the end of the war in Germany. Some photos I've seen show M42 jump jackets with M43 combat trousers - mixed and matched. Riggers would modify the M43 combat trousers to jump trousers by adding larger cargo pockets and web tape or canvas strip tie-downs. You see this in the Rhine jump.
Soldier Story's new "US WW2 Airborne Jake McNiece - Filthy 13" is an excellent example of a member of the 101st as he would have appeared during the D-Day invasion. Uniform is correct, the M1942 jump jacket and trousers in the freshly issued slightly brownish green color. This uniform has been Rigger modified with green patches and cargo pocket trim added from treated canvas, the whole uniform was gas treated prior to the drop for fear the Germans would use poison gas. After D-Day these same uniforms will have faded considerably from repeated washings to get rid of the stinking CC2 anti-gas chemical that was used to treat them. That difference alone can tell you if your paratrooper was present on D-Day or not. That's why the subsequent M42's look a different color from their original D-Day issue.
I hope this at least gives you a rough idea of what you want to look at to make your decision on what figure to buy. Finally I'd advise you to read the reviews here on OSW, Monkey Depot and Michael Crawford's site:
Michael Crawford's Review of the Week ! have been really helpful for me when I'm considering buying a particular figure or even for parts (which is what buy most often). These are accompanied by photos that give you a good look before you buy and the critisism is for the most part by knowledgable people.
