I've been using mint since Sept 2011 and YNAB since Feb 2012. I continue to use both, but YNAB is my daily tool that I couldn't live without, while I check mint once every week or two just to go in and look at my investments section. That's really the only thing mint does for me that YNAB doesn't. Mint automatically uploads your investment information and shows you your current value in each account and the total. I like looking at the graph and seeing the upward trend. I've mimicked that in YNAB by tracking our TSP and IRA accounts as Off-Budget accounts and then going into Reports and looking at it there, but I only update those numbers monthly so it's not quite as much fun as mint (which is daily). However, I've also had multiple issues with mint not syncing correctly, and have recently run into a new one which affects my investments. :-/
I absolutely love YNAB and cannot say enough good things about it. I find it to be infinitely more flexible than mint, and not nearly as clunky. If you want to add money to a budget category, you click on the appropriate box, enter the number and you're done. In mint, you have to go to the budget tab, click on "details" of the category you want to edit, enter the number, click done, and wait for it to reload. Very annoying when you want to set up a new budget at the beginning of the month. Mint is good for hands-off tracking, but terrible as a budgeting software.
One thing I love about YNAB that I haven't read anyone yet mention is the Reports section. In here, you can look at your spending trends by category, by account (checking vs. cash), by month, etc. My favorite is the Net Worth page (of course). Once you have enough data, you can compare this May's spending to last May's spending, or this quarter's spending to last quarter's spending. I used to love mint's visual charts, but YNAB revamped their Reports section with YNAB4 that came out last summer and now it's very user-friendly and very flexible. I've also been extremely impressed with YNAB's customer service- they are stellar and outstanding and I can't say enough good things about them. They also solicit feedback for suggestions/improvements, and the owner, Jesse, periodically sends out updates and basic courses with a great writing style and sense of humor. I personally do forecast my budget since DH and I have extremely regular income. I've actually budgeted out through April 2014 since we have a project we want to complete, and I can gaze at our expected net worth six months from now. :-) I would definitely at least try YNAB. If it doesn't work for you, then fine, but I think you're missing out if you don't even try it.