As far as my personal comfort is concerned, I don't care much what is the default, as once this or one of the equivalent RFEs get implemented (which I'm sure will happen soon), it will be a matter of changing an option and forgetting forever. The important thing about defaults is that they should be good for new players, as old-school players like myself know how to fish for configuration options and can adapt.
However, I have seen in the forums that there is really a lot of people that prefer the classic UI layout, of course some of them are veterans but I suspect even newbies that try it tend to prefer it, as there are a lot of people I've never seen in the community before asking for this option. It would be a pity that newbies who don't know how to change the default were stuck with a suboptimal layout, that's why I think the default should be reconsidered.
Note that "reconsider" could mean making usability tests with a few newbies, or maybe a poll, etc., and perhaps the conclusion would be that I'm wrong and most newbies prefer the new UI, while old-school players only prefer it due to inertia or nostalgia. I don't have data to back my hypothesis, just an impression based on seeing a lot of people asking for the classic UI, but this of course may be biased (who knows how many other players prefer the new one and are not speaking). However, the devs could obtain such data to make a reliable guess about which UI is really preferred.