For anyone seeking an alternative, I've found 2 which I like:
ExpanDrive is a cloud drive syncing client which supports several cloud services, including DropBox, Google Drive, OneDrive, box and some others. It's a bit pricey though, $50 for the current version license and an extra $38 to get lifetime updates. But it has the benefit of being a single client for Linux, Mac and Windows if you're not ready to move away from DropBox.
https://secure.expandrive.com
insync is a bit more reasonable, $30 per Google or MS account for a lifetime license, but only supports Google Drive and OneDrive. So if you're fed up with DropBox enough to be done with them, this could be a decent solution. Google Drive gives you 30GB for free, so that could offset some of the cost. Personally, I paid for the 2TB upgrade on DropBox before I realized I would have to dedicate a potential 4TB of drive space to have syncing enabled on my dual boot Linux/Windows device.
https://www.insynchq.com/
Others have suggested some open source options, maestral looks pretty cool, but doesn't have a Windows client. I worry about sync issues between Windows and Linux if I'm using a different client on each. If anyone has found some alternatives, maybe free ones, leave some links?