Proportional, for an e-ring.
I wouldn't mind owning a showy ring (as big as possible) for a cocktail ring that is fun and obviously cost $$$$, but to me, that's not the purpose of my engagement, which is about the love and what a young husband can manage in the budget. the bigger rings are for later, and show success and all that and are fun to pull out in the evenings for 'occasions' but for me, not for every day. For the opera or a big fancy formal party, go as big as you want, wear a four or six or even sixteen carat diamond if you can afford it (though if it's sixteen carats, you probably want an emerald cut, not a round). But an engagement ring is worn every day and after a certain point, it looks odd.
i guess I'm old school.