I'm Finnish too, from the Häme - Satakunta region (SW Finland), so I thought I'd drop a comment or two. I think I speak fairly "normal" Finnish, when it comes to dialects, which we have many, despite the small population... I think it's got to do with the population density - or the lack of it: we have 5 000 000 people in a country as big as Germany (with over 80 million people). Well, there isn't a dialect here that another Finn wouldn't understand, so I think Finnish is fairly standard compared to many languages.
I'll start with the voices. I prefer Esa's voice over the others, because Martti sounds a bit sloppy or fuzzy to me, and Heta doesn't sound like a woman at all (or human for that matter). So I'd choose Esa as the enunciator of exemplary Finnish.
I followed the advice above and tried the different speeds, and I find that Esa's speech is reasonably realistic when you put it on fast speed ("nopea") and avoid all the other buttons, like the male hormone thingy (which just lowers the voice and seems to slow it down somewhat). Then try putting in something like "jääkäriryhmä" (jaeger squad), "panssari" (panzer / tank), "konekivääriryhmä" (MG squad) or "tykistöpatteri" (artillery battery) and you should hear a reasonably realistic Finnish pronunciation. Like the others, Esa does sound a bit strange, but when he's speaking quickly, the odd stress (that he puts on the different syllables of a word) is slightly less strange. Of course, if you want to learn how to say the words, you can pick out the syllables better when the speed is slower (tavallinen = normal, rauhallinen = "calm" or "careful", but it sounds like he's making a point or teaching somebody how to enunciate).
Note that Finnish is "spoken like it's written", so you don't need to learn how to pronounce the syllables in more than one way.
In short, I'd click the following buttons, when using the program: Esa, normaali puhe, nopea. I hope that helps!
For a bit of fun, you can make Esa speak the longest Finnish word "epäjärjestelmällistyttämättömyydelläänkäänkö".
(It's actually a question that doesn't make much sense, but it is grammatically acceptable.)
Oh, and do note the effect of Scandinavian letters that are often omitted in computer games: "jääkäriryhmä" differs from "jaakariryhma" in a clear way. In fact, the latter sounds like Estonian to me.