While my ubuntu is still downloading, I took family picture of my equipments. Bellow few fast thoughts;
E71 is warrior, nothing more than great phone. Suffers a bit from Symbian syndrome, but does a great job with voice and sms communication. I wish I could have jabber integration in this as in N900.
3720C is basic without worries to break it down. I just love S40 interface, making it fast and furious to use. But again, lacking with decent capabilities to communicate in other that operators network. This is backup phone for me, in case I get kernel panic with my N900.
N900 is currently my main phone, I wish Nokia would understand and release full potential of meego (maemo). Now I can handle everything with this phone, from GPG to SSH and communication from voice, sms to jabber and skype (which I do not like).
Last is N97 mini, as I posted earlier - it should act as wakeup call to Nokia. Do not play with symbian anymore, try to make it anything more than it's capable.
So, my SIM flies between these phones quite often, depending what I need to explore.