Brian (from the Hobbyden - see link in the right column) has done a nice shot to compare them both and allowed me to use these pictures (thanks, mate!).
First off, Brian started to show us what comes with the cheap box of Caesar's 1/72 "modern US" set. There are some really nices poses included and for the really good price of just a single box they might be good for a lot of people to get started with "moderns". The cost of a single box of Caesar figures should be lower than 10 Euro and it holds 42 (!!) figures. Caesar figures are in perfect 1/72 scale. What Brian doesn't like about them are the helmets - in his opinion they could have been done better.
Now with the second pic, Brian shows us that Matt's pewter figures (Elhiem) are a perfect match of the plastics. While they are a tad chunkier (due to the material used) in my opinion they would mix perfectly. After all, humans come in different sizes, too. I have an US Army force that uses both, pewter figs from various sources and also Caesar's plastics. While opinions differ, I think especially the plastic sets from Caesar are a good way into the hobby. You can also get "insurgents" in a box of around 40 figures. What troubles me with the Caesar plastics is the strange way how they include weapon options into their sets - the "modern US" for example includes the heavy .50cal sniper rifle but no spotter figure. It also has no M249 SAW included but M240 Medium MGs.
To build correct forces with those boxes you'll need to get yourself the other sets available from Caesar - just for some SAWs. :-( But when you do, you get various weapon options for a good price. Caesar plastics aren't as flimsy as others (Revell for example), they paint up rather nice.
