I love miniatures at the gaming table, especially the wide variety of prepainted plastic figures you can get these days. My D&D campaign features the deployment of a wide variety of D&D, Heroscape, and MageKnight figures. And a Star Wars or Heroclix figure makes a guest appearance once in a while as well. Sometimes I knock myself out sorting through my large pile of little plastics dudes, looking for the exact right guy. But the thing I always try to remember is that the criteria for "the exact right guy" has very little to do with the weapons, armor, race, or gender the figure displays.
When selecting a figure for the gameboard, you really only need to consider two things. First, make sure the figure functions properly as a game marker. Is it easily differentiated from the other figures on the table? Secondly, look at the overall message suggested by the appearance of the figure. For example I've played two different PCs in the World of Alidor campaign, each of which was represented on the table by a Wizards of the Coast figure.. For mmy first guy I used the Elf Swashbuckler while the Shifter Barbarian usually stands in for my current guy. Note that Randolph of Falcon was neither an elf nor a swashbuckler. His hair wasn't blond and he didn't wear leather armor. But the pose and corresponding attitude of the Elf Swashbuckler was just perfect for representing my devil-may-care Favored Soul/Bard. Similarly, the Shifter Barbarian just oozes "I'm a rough-and-tumble bastard here to wreck your shit" and that's my new guy Osric in a nutshell.
Let's look at a less personal example. Say you're reffing a Traveller campaign. Your PCs are mucking around the spacelanes in a standard Beowulf class Free Trader, probably a limpy old model that's several decades old and many months in arrears on the loan payment. Suddenly, a massive Azhanti High Lightning class cruiser appears on the radar. Like me, you absolutely enjoy using miniatures as a way to scare the crap out of your players. You don't have any Trav ships (and sadly, they never made an AHL figure), so you break out some old Star Wars toys, from the excellent Micro Machines line. These two figures make the situation abundantly clear to the PCs: Before the session began many or most of your players had no friggin' clue how big and powerful an Azhanti High Lightining is in relation to their wee tramp freighter. But now they know, and they're scared. Without a single line of description, you've conveyed the situation quite nicely simply by picking the right minis.
But let's say you want to send a message to the PCs, something besides "The Evil Empire is on your ass and you're quite resoundingly fubared." Let's say you drop these two figures on the table instead:
That's a horse of a different color, isn't it? The players might come to the conclusion that rather than running like a mofo, perhaps they could discuss the situation calmly and rationally. Or maybe get in a fistfight with the captain of the cruiser. Or maybe a female PC could reach some sort of understanding with him. Either way, you sent a completely different message to the players without saying a word. And not just about the captain of the opposing ship either. Both figure choices also convey totally different messages about the nature of the setting. In which example would you rather be busted for smuggling? I'll take my chances with the Imperium that employs Captain Kirk, thank you.
One more spaceship example. Same basic situation, but again a different figure choice for the big Imperial ship.
Like the first example, the players are probably going to assume that this cruiser is less than friendly. In addition they might be wondering if the crew of the vessel is even human. But they do know that being frozen in carbonite is the least of their concerns right now.