Interesting thread. The last time I seriously considered jumping ship, maybe a year ago, I evaluated about 30 apps. At that time, the main problem, as it still is, was the lagging issue. Evernote can sit there in the background all day and do nothing, yet as soon as I click on it to search for or create a note, it says, "Hey, I need to do a bunch of stuff, right now. And this would also be the perfect time to sync, rather than when I was idle."
The only serious contenders for me were Google Drive, OneNote and Nimbus. Nimbus had the most potential, but as some have said, it's a bit buggy too and moving from one buggy app to another doesn't look like a solution. I will keep an eye on it long term, however.
As far as porting to something else, there are the importing tools of Nimbus and OneNote, and as DTLow said, export everything to HTML and go from there is a great solution. All of the import tools, are of the square peg in a round hole variety, so, while they are quick and easy, the results aren't desirable.
Having said all that, I have been ready, willing and able to jump ship for a while. To that end, I keep current backups and am slowly creating parallel systems. One thing that has made that easier is getting away from the Everything in Evernote mentality. For years, all important emails have been forwarded to Evernote. Why? My email system is just as capable of organization, searching and cross-platform ability. So, I have been creating rules and filters in Gmail and stopped sending everything to Evernote.
Note taking is still done in Evernote, but moving that to any other platform would be quick and easy.
This leaves document storage. As much as I hate it, the best solution for me is OneDrive. For several reasons, I have an Office365 sub, which gives me a 1TB storage limit. My current storage after 10 years in Evernote is 5Gb. So I am slowly copying PDFs, etc. to OneDrive and creating systems in IFTTT to duplicate things going forward. I don't need OneNote to access any of these files, but if, at some point, I drop Evernote, I could pick up OneNote without a problem. It has some nice features once you learn the way it syncs, etc. And porting things slowly and methodically instead of some radical, I have to leave right now mentality, allows me to rethink and restructure the whole mess. With OneDrive, I can create the hierarchy that makes sense to me today, and if I go to OneNote, I can rebuild my tag structure rather than just porting everything over. As others have said, if Evernote shut down tomorrow, which most of us don't believe will happen, I have the desktop app and all my data, so I can take as much time as I want porting to another system. Which leaves me with the only problem I see with OneDrive, but one which has an easy solution. It's all in the cloud. I will have to create some system to replicate it locally, along with my external hard-drive and cloud backup systems.
And when I say drop Evernote, I mean stop paying for it. Unless they go out of business or have a security problem, there would be no reason not to maintain the free version as a backup. I don't plan on ever moving everything in Evernote to another system, so having things where I can always find them makes it a no-brainer.
Evernote works for me. I like it. I don't want to leave it and don't have to right now. But the management and direction of the company has been flaky for a long time now. I don't know if they can, or even want, to turn things around. But right now, I have until April to decide whether to pony up another fee.