score:7
Roads in Finland are good, although not luxurious. Helsinki-Tampere is all motorway, as is the last part of Lappeenranta-Helsinki, the rest you'll be driving on two-lane country highways. In short, any of those cars should be just fine.
There are a few quirks to driving in Finland explained in detail at Wikivoyage, the main one being that you always need to keep your headlights on. Winter driving can be sketchy, so four-wheel drive is a plus, and winter tyres are required by law from December to February, but if you're driving, the rental agency is responsible for this... and if you're a tourist, you're probably not planning a driving trip for mid-winter anyway!
Upvote:3
The only addition I'd make to the first statement by @jpatokal (that any of those cars are fine) is that whatever rental company you go for I've found it best to get the level up from the cheapest.
The lowest usually have smaller engines (not always a problem) but will most likely have very limited features. I've found that often now if you get the next level above the cheapest you get air conditioning, electric windows, auxiliary/line-in 3.5mm jack for audio and now even Bluetooth, which is great. Just be sure to take a male-to-male audio lead to connect your phone.
The extra bonus which I've managed to get a couple of times is cruise control. It's certainly not a common occurrence, but for the long monotonous roads at slowish speeds it's nice to be able to stop yourself speeding.
Upvote:5
The C-1 is a very small car; if you can deal with that, go ahead. Other people take much longer trips with this type of car.
If you want more comfort, definitely go for the DS-5.
And if you want a Beemer, well, you won't have to ask further.
However, normally, the car model is not guaranteed; you pay for a specific category.