I do try to give my models within the same army the same TYPE of basing. mostly either grass or areas where the grass has been worn down, which works fine. However, I do also try to theme the base with the creature type. I really need to get back to them but my Fimir have a more swampy base to suit their characters, where when I figure out my Plague bearers, they will have a plaguey base.. but I just can't figure that one out right now.
I think I've a similar approach to Manic. So each race does have a style of base to hopefully provide a bit of uniformity to the "army". Broadly however all my fantasy stuff is on muddy grass with nothing too wacky that it wouldn't fit on most grass/scrub boards. Very broadly speaking: Undead are Vallejo Dark Earth with short 1mm patchy "dead grass" and brown/dead tufts. Nurgle are Vallejo Dark Earth with more standard autumn/ grass and swampy tufts. Orcs/Gobs are Vallejo Russian Mud with summer static grass and more conventional tufts. I don't mind a bit of decoration on the bases, so the ones I did for my Beast of Nurgle
can be seen sans-beasts here (although those are Russian Mud rather than Dark Earth)
All my 40k stuff is on fairly plain Vallejo Dark Earth textured bases with a bit of highlighting and the occasional one with a tuft or bit of barbed wire or something. That was with a view to a board I will (maybe) one day make (I've done the mini tile mockups!) and also so they wouldn't jar too much if used in more urban settings on walkways and so forth.
I'm not a huge fan of seeing huge bits of terrain walk across the battlefield, but I do quite often pop decent chunks of stone on my flying models to help weigh down the bases and lower the centre of gravity. So (since I'd not otherwise post it) I'll use this more modern Nurgle mini as an example of the kind of thing I do:
I also tend to avoid clear flying stands now, although I did base my 40K jetbikes and speeder on them (although with the newer larger diameter bases) as I find a bit of brass rod painted matte black disappears more than a bit of acrylic 2-3× the diameter that reflects the light. I'll finish basing my other jet bikes (ended up with a few) the same for consistency however now.
I think if you collect and paint more than actually game then nothing against modelling your miniatures on very scenic bases for display, but
personally it'd jar too much for me on a gaming board unless it was like Fimm mentioned designed for a specific board. I do think certain armies tend to lend themselves better to styles of bases. So were I (keeping with our examples) doing a Tomb Kings army I'd probably model the bases leaning more towards a desert-esq feel, but not so much that it wouldn't work on your typical "green field", so much like you might make bases a bit more swampy, but not crazy. The wildest I've seen are probably where it's all water bases, now they do look odd when on a normal battlefield.
The only other basing decision I actively make is a tend not to base larger things like tanks where they are very stable. So I'll base a chariot since from youthful experience they do tend to otherwise fall apart, the same for bikes which spend half the game on their sides. I'm not a fan of seeing Rhinos on bases and things that are very solid otherwise - it's probably something against huge bases since I really dislike seeing Titans on huge foot wide bases. I expect if I head over to
Beachead in Feb I'll see lots of over the top basing, seems quite common for flyers in 40k to be moving with half a building under them and so forth! Speaking of which if anyone is going to Beachead give me a shout and I'll try to time going to say hello.
