IMO, you should be looking at something along the lines of a Vanguard Target Date fund.
Keeps you from being worried about balance, timing, etc. Just invest and rest.
The funds are actively managed and perform very well. Fidelity has a few good choices too.
I'm a big believer in a 'hands off' approach to investment, leave it to the pros.
Of course, you'll want to ensure the rest of your asset base is well diversified as well.