I have quite a lot of 10mm WWI figures. Most of my figures are Pendraken, with some Magister Militum (mainly French for early 1914).
The time to paint figures is very quick! And you can get lots of the big guns and tanks etc on the table without breaking the bank.
Some of my late war British

Holt Tractor and 8in gun

Early war French Artillery

Rules wise I've played a bit of Great War Spearhead - which seems very detailed, but takes quite a bit of understanding, which as WWI is an ancillary period for me makes it a bit hard when you only play the rules occasionally.