The policy you quoted suggests you deposit 6% minimum. That $6,000 will cost you $4,500 due to the tax effect, yet after the match, you'll have $9,000 in the account. Taxable on withdrawal, but a great boost to the account.
The question of where is less clear. There must be more than the 2 choices you mention. Most plans have 'too many' choices. This segues into my focus on expenses. A few years back, PBS Frontline aired a program titled The Retirement Gamble, in which fund expenses were discussed, with a focus on how an extra 1% in expenses will wipe out an extra 1/3 of your wealth in a 40 year period. Very simple to illustrate this - go to a calculator and enter .99 raised to the power of 40. .669 is the result. My 401(k) has an expense of .02% (that's 1/50 of 1%) .9998 raised to the same 40 gives .992, in other words, a cost of .8% over the full 40 years. My wife and I are just retired, and will have less in expenses for the rest of our lives than the average account cost for just 1 year.
In your situation, the knee-jerk reaction is to tell you to maximize the 401(k) deposit at the current (2016) $18,000. That might be appropriate, but I'd suggest you look at the expense of the S&P index (sometime called Large Cap Fund, but see the prospectus) and if it's costing much more than .75%/yr, I'd go with an IRA (Roth, if you can't deduct the traditional IRA). Much of the value of the 401(k) beyond the match is the tax differential, i.e. depositing while in the 25% bracket, but withdrawing the funds at retirement, hopefully at 15%. It doesn't take long for the extra expense and the "holy cow, my 401(k) just turned decades of dividends and long term cap gains into ordinary income" effect to take over. Understand this now, not 30 years hence.
Last - to answer your question, 'how much'? I often recommend what may seem a cliche "continue to live like a student." Half the country lives on $54K or less. There's certainly a wide gray area, but in general, a person starting out will choose one of 2 paths, living just at, or even above his means, or living way below, and saving, say, 30-40% off the top. Even 30% doesn't hit the extreme saver level. If you do this, you'll find that if/when you get married, buy a house, have kids, etc. you'll still be able to save a reasonable percent of your income toward retirement.
In response to your comment, what counts as retirement savings? There's a concept used as part of the budgeting process known as the envelope system. For those who have an income where there's little discretionary money left over each month, the method of putting money aside into small buckets is a great idea. In your case, say you take me up on the 30-40% challenge. 15% of it goes to a hard and fast retirement account. The rest, to savings, according to the general order of emergency fund, 6-12 months expenses, to cover a job loss, another fund for random expenses, such as new transmission (I've never needed one, but I hear they are expensive), and then the bucket towards house down payment. Keep in mind, I have no idea where you live or what a reasonable house would cost. Regardless, a 20-25% downpayment on even a $250K house is $60K. That will take some time to save up. If the housing in your area is more, bump it accordingly.
If the savings starts to grow beyond any short term needs, it gets invested towards the long term, and is treated as "retirement" money. There is no such thing as Saving too much. When I turned 50 and was let go from a 30 year job, I wasn't unhappy that I saved too much and could call it quits that day. Had I been saving just right, I'd have been 10 years shy of my target.
