Well the time to invest is when the coin is near a low, and is in red. That way you can rest assured you bought at the lowest price (or close to) as you could.

IMO the best ones out of the bunch are:

*WAVES
*Monero
*Steem
*Antshares
*Stratis

I would stay away from Ripple, Dash, Mainsafe, Golem - but that's just me, others would disagree and that's fine.