I have Mint 17.3 on two laptops, but your Ubuntu with Cinnamon setup is tempting. Any downsides?
There is no downside at all. The is the Long Term Stable LTS Ubuntu 16.04. You can test it on you laptops without installing on the hard drive. Create a live USB stick with UNetbootin. Boot your laptop and make sure the hardware works before installing on the hard drive.
Mint 17.3 uses the 3.19 kernel and Ubuntu 14.04. Ubuntu 16.04 uses kernel 4.4.0 and has systemd.
But I like the larger support team behind Ubuntu. It gets earlier updates and earlier security updates.
Firefox 47 just came out a few days ago and already the Ubuntu team has pushed that update to my computer.