I'm happy to go whichever way, but I think my preference generally is to split the bill evenly - much simpler, and it seems when I'm out with friends (recently anyway) people end up having about the same amount of drinks, courses, etc.
I have been out with large groups before where everyone just put in for what they themselves ordered (or what they think they ordered several drinks on), as the bill got passed around the table, and then the last person got stuck making up the difference because someone along the line (not knowing who) didn't put in enough or didn't add some for service charge/tip, etc. Which then becomes a stressful thing either to figure out who didn't pay sufficiently, or the last person having to suck it up and pay more than their portion. Complicated and awkward! So it's not just splitting up evenly that can leave people feeling ripped off, if you see what I mean?
And I agree with chary about calculators.