Do you find yourself in need of that 5% you're currently putting into your 401K? Or, like me, you find that you 'hardly notice' that money wasn't in your paycheck because of the tax offsets? (because 401K funds are taken out pre-tax). If you find yourself needing those funds, you might consider a retirement vehicle like a Roth IRA where you can withdraw CONTRIBUTIONS at any time for any reason without penalty. If you are single, you must have a modified adjusted gross income under $133,000 to contribute to a Roth IRA for the 2017 tax year, but contributions are reduced starting at $118,000.
Does your 401K program offer a company match? If so, DEFINITELY contribute at least up to that match amount - that's FREE MONEY for use in retirement. Beyond that, and depending on your answer to the first question... realize that YOU'RE YOUNG. Your 50+ year old self will THANK yourself that at the young age of 28, you were smart enough to start contributing to a 401K. The older you get, the more likely you will want to contribute the maximum yearly limit to your 401K account - for 2017 $18K, for 2018 $18.5K (AND from 1/1-thru-4/15, one can contribute to their PRIOR YEAR 401K/IRA/Roth IRA account if they belatedly decide they want to MAX OUT their savings).
That yearly savings opportunity can't be recovered - use it or lose it. I've only been maxing out my 401K for the past 4 years. BUT... I *WISH* I had maxed out my 401K savings for the past 20+ years of my working career. If I had done so, I would have over $284K in contributions alone - not even considering the ROI of INVESTING those contributions @ 10.58% average return over the last 15 years... or an additional $30K.
As for what to invest in... VTSAX (Vanguard Total Stock Market Index fund). Your 401K plan may or may not allow you to purchase Vanguard funds, but if they do, consider the Total Stock Market Index fund. (to learn more, read JLCollinsHN's 'stock series', or his book "The Simple Path to Wealth").
All the best,
(and remember... you're asking the advice of strangers on the internet. Use your own judgement, and the advice of your investment adviser.)
MFB