WW1 Skirmish

[Miantanomo]

Mud and Blood is my choice. And scaled down, its still good. Doesn't bog down and still very playable and enjoyable.

[Metternich]

Mud and Blood also seems to cover well the factors that make WW I what it is and is not just a generic set of rules (e.g. the distinction between the characteristics of bombers and trench cleaners).

[Cessna]

My favorite is "The Great War" set of rules by Warhammer Historical but you will pay an arm and a leg to get them.

Another good set is "Through the Mud and the Blood" by Two Fat Landies. Caution though...if you want a bound volume you'll have to search. The website indicates you are buying a hard copy but in reality it's a .pdf. I ordered the rules and a supplement and got .pdf copies even though the description clearly indicates hard copies. I contacted them about it yet haven't heard back from them.

Another good one is "Contemptible Little Armies" and less hassle to come by!

If you're ever in Denver, let me know. I've got the rules and plenty of WWI figures painted and ready to go.

[Hammers]

I can recommend Triumph and Tragedy - it's perfect for the size you're talking about and can be used for games from 1900-1930's and if colourful is what you want there is a Pulpy feel to it as characters are very important.  I played WW1 with the author a few years ago and I had a lot of fun.

I also have Through the Mud and the Blood, it's a bigger scale and is more about command and control.

I second this. If you by 'characterful' mean some emphasis on leaders and heroes, I'd say this is your best choice.