You need to decide on a budget and go from there. Obviously, if your budget is $50, then the iPod Touch is out of the question. On the other hand, if a gift worth $225 would be appropriate, then the Shuffle will not suffice. (I'll let you translate the currency.)
In the US, iPods seem to be popular corporate gifts. The Nano and the Shuffle seem to be the most popular gifted models, but that may be because of the price ranges. The Nano has a couple different storage options. I wouldn't spend extra on the 16gb Nano model. It's too close in price to the entry level 8gb Touch, which is a much nicer device. 8gb is still plenty of storage space for an iPod.
Although some diehards will probably object, I'd suggest staying away from the Classic. Its antiquated technology, that is strongly rumored to be discontinued this year. It contains a hard drive with moving parts which is being phased out by solid state memory storage which continues to drop in price.
You can't really go wrong with any of them. Just decide what an appropriate amount to spend would be and get the model that matches your price range.