My OOO is almost always “I’m out of the office and will be returning on x date.” My email sig has instructions along the lines of “for questions on x, email this list” for a couple of the more common areas people would contact me about that might need an urgent reply (as the lists go to more than just me, obviously), but most people have finally figured out to contact those lists to start with, anyway. If I were in the middle of a project or something that needed to be moved along in my absence, the project teams usually know when we’re out, but I’d put a back up in that case, if needed, but generally there’s not much to be gained by a longer OOO from me.
For example, if you don’t clearly state the dates you’ll be gone, your office coworkers and clients might send you multiple emails, clogging your inbox and making it difficult for you to catch up when you're back. And if you don’t include the name and contact information in your outgoing message for the coworkers who can help in your absence, your well-earned vacation time might get in the way of ongoing projects at the company.

I’ll reply to your message promptly when I return. Should you require immediate assistance, please send an email to [contact name] at [contact email] in my absence.
It’s common practice to prepare an email vacation autoresponder for when you are going to be away from work for a lengthy period of time. But in many cases that isn’t enough to give you – and those who may be wanting to reach you – peace of mind while you are gone.