Which to buy?

As I was saying, very tempted to buy a new phone after using one of my student's phone.

Found the following 'free' phones from Singtel. Which one should I buy?

Nokia 2626	Samsung M300
Sony Ericsson K610i	Sony Ericsson K510i
Sony Ericsson W200i	BenQ Siemens S81
Samsung Z370	Motorola SLVR L72

So, anybody wanna give me some advice?