2 x 30 also gives you a nearly 100' rap. One 40m rope would be better for climbing some alpine rock routes, but it gives you only a 66' rap.

The answer to OP's question is very route specific. He...

Depends. For most of the glacier travel we've done over the past 30 years I'd get a 60m twin and cut it in half to make two 30m ropes. If you sell one you'll eventually regret it. Take one 30m rope...