I am an IT engineer, so please take my advice with a grain of salt as IT is a bit different in terms of employment.

Money may not mean a lot once you get past a certain yearly salary. I am in a place where I'd give up 10% of what I currently make in order to get more vacation. 10% of my paychecks is a good amount of money too...

Retirement benefits are good, but you're only 23. Start saving early and remember that there are other choices besides 401K. While 401K is the best, consider Roth IRA if the plan provided by the company sucks. I can tell you that you will not be working for the same company until you're 60. In IT if you don't have a new job every 5-7 years you're setting yourself up for unemployment benefits. I don't know if mechanical engineering is different. If you start saving now, you should be all set.

Life is too freaking short to get caught up in a daily routine of a large company. Look for the atmosphere and a career path. Do you want to invent things or be a pencil pusher? Do you like to do things that mean something to you or do you just want a nice title? How do the offers differ in terms of time off? I would be hard pressed to take any job that offers fewer than 3 weeks of paid vacation time.

Finally, remember that nothing that you do now will matter in 50 years. Well, unless you're about to figure out how to cure cancer or AIDS. Find a job that allows you to make a living and enjoy the life to its fullest. The rest is just details