I found MMM in February 2014 and starting using Mint in March 2014. Mint appears to have a few limitations, so I was thinking of upgrading to YNAB. I just started the free trial on YNAB, but I have found some limitations that I was not expecting. The first limitation is that it can't find my primary checking account (Kauai Community Federal Credit Union). This checking account includes the majority of my transactions. Mint was able to recognize the account, but not YNAB. I have two additional concerns. One, I wasn't able to upload my student loan account. Two, I don't know how to enter the value of my two rental homes so I can track my net worth.
Do you prefer Mint or YNAB and why?
I use both but Mint more regularly. My wife is more responsible for YNAB and keeping things up-to-date there. YNAB is a lot more manual entry as that's what the intention of it really is - to keep a close eye on your inflow/outflow of cash and accounting for every transaction pretty much ("give every dollar a job" is one of their mantras). I find it to be tedious but my wife enjoys doing that kind of stuff which is why I leave it to her. I should probably get a little better with it but I guess I'm just lazy.
Plus, I'm more of a big-picture kind of guy when it comes down to this stuff, so I like to use Mint for those purposes. Mint provides a higher-level view than YNAB does IMHO. I would say that it's probably good to be using both if you can. Mint, overall, is pretty useful with giving you dashboard views of net income, spending, etc.... where it sort of lacks though is with investment views. For that, I use Personal Capital. It may seem like a lot of work and trouble but it's actually not - the bulk of your time up front will be spent adding accounts... other than that, you often have to go in and change categories for transactions but that's about it. You can set "budgets" in Mint too, which are more just a visual bar graph of your budget ceiling limit and how much you've spent. It may not keep you quite as accountable as YNAB does.
I would argue that each of these apps is good for it's own unique purpose, and using them together is not a bad thing.