I would suggest building for 6.2 (since it's stable) in parallel with 7. The first alpha of 7 is out and I think there will be further announcement at the NAS, but you should question whether you need to be on the cutting edge or not and how much bleeding (as an outcome of being on the cutting edge) you're comfortable with.

Keeping an eye on LR7 development and changes is important, but right now it's a bit ambiguous when it will be ready.

I'd recommend going with 6.2 simply because it will still be around and stable when you go to production. You can always look at 7 when it comes out and look into a migration/upgrade path, but you won't be held up in the interim.

I agree with David.

As it was announced in Spanish Symposium last week, Liferay 7 CE would be released in Q1 2016.

If you are planning to migrate to Liferay 7, as David said, I would start first in 6.2, as it is stable right now, and will give you time to think on the approach for 7.0 while you're in production. If you are developing MVC portlets in 6.2 I think it won't be painful to make the needed changes for 7.0.