Sveikas! The Hexagon looks like it has a slightly better rear derailleur, but overall they all look pretty similar. None of them seem to have very robust wheels, so I wouldn't use them for any jumping or big bumps without planning on buying new wheels.
The Radius Orange in the link seems to be better quality, BUT has a non-suspension fork. This will last longer and be more durable, but you will have to use your body position to "absorb" bumps such as tree roots on the trail. For riding on pavement and gravel, a non-suspension fork should be OK. Remember, suspension forks only became common about 10 years ago.
The white bike in the photos actually looks the best (but will need pedals! ). Having a disc brake in front is nice, since most of your braking force comes from the front wheel.
The "star blocks" are called the "crankset" (front, includes gears and crankarms) and "cassette" (rear, includes just the gears) here in the USA. Sheldon Brown did a lot of work on translating bicycle terms to different languages, but I don't think he got to Lithuanian. A partial list of some of his articles in some different languages is here: http://www.sheldonbrown.com/translations.html