As long as you want to let the manufacturers dictate what poses you're gonna use, I reckon there's some decent resin figures and such... Verlinden makes some of, IMHO, the best ones. But I buy damn few of 'em, simply because I can't stand being locked down into using the same poses everyone else is using...
Buying you some Tamiya, Revell/IRC, and Dragon sets, you can afford to have a lot of figures to select choice body parts from and create your own poses, which adds much more flexibility to a diorama-builder's story-telling abilities... By buying some after-market heads, you can create many more "personalities" as well...
I know that there's some guys here that are absolute masters at figure-painting, and that their work is, to say the least, outstanding, but the truth of the matter is that you don't have to create figures that you'd swear were about to talk to you in order to tell a good story with them... Base-color, with some shadow and highlight, a face with a five o'clock shadow, some shadow, and well-placed slits for eyes can be as effective as anyone else's work... You just have to remember to CWR (crawl, walk, run) when it comes to figure painting... A pair of High-dollar figures will not save your diorama if they have a crap paint-job... On the other hand, cheap figures, well-posed & placed, with well-done paint-jobs can be the saving grace of an otherwise mediocre diorama...
My suggestion is to forego the high-dollar figures, buy up a half-dozen or so Tamiya or Dragon figure sets of at least 4 figures each (6-8 would be better), a good razor saw, pin-vise with a #78 bit (for drilling holes to insert wire "joints"), putty, and start chopping up your squaddies at the joints... If you can get 4 or 5 good poses built out of a dozen figures, you're about par for the course on figure conversions, and no one will have any figures like yours anywhere... And don't forget to ordder some generic heads... They'll go a long way for little money...
Oh yeah, one more thing... Don't sweat whether you're doing "modern" figures of WW2 or whatever.. Although the uniforms change, anatomy doesn't...Also,adding action & drama to your dioramas is easy when you learn to keep your figures in off-balance poses (even mid-air sometimes)... Quiet scenes, although usually more effective than "shoot 'em ups", can get old after awhile (how many mail calls/map-readings/busted track/flat tire/taking a leak/ dioramas can one do, anyway?), so don't be afraid to get a little crazy now & then...