The Admiral fund is a broader market fund, but may have a larger required initial deposit. You need to look at some of the details.

You generally want a balance in your accounts. There is a very general rule of thumb, which is that as you age, less of your portfolio should be in stocks. So, say at 33, say 70% of your retirement funds should be in stocks, the rest in bonds and money market. If one of the available funds is labeled something like "Target 2050" then that is usually a combination of funds targeted at people retiring in 2050. It does the balancing for you.

So - things to look for. 1) what index does it follow if any? So VFIAX is the S&P 500. Total Market is even larger.

2) what is the initial deposit? It does you no good to be looking at funds with an initial funding of $10K if you are putting in $1K.

3) look at the top ten holdings. How concentrated is it?

4) what is the expense ratio? And are there any fees (although this is unusual in a 401K) All things being equal, if you have to funds that are essentially the same - say two S&P500 index funds, you want the one with the lower expense ratio.

5) and this is actually the most important one and has nothing to do with the fund you put things in - what, if anything, does your company match? If they are going to match 100% of 3% of your salary, you could stick that money in a money market fund and be better off than not doing a 401K at all. Because you are doubling your money just using the 401K. If they match 50% of the first $2K then, seriously, where else would you get $.50 for every dollar you put in - put in $2000 and at the end of the year it's $3000? - sign up for that sucker! If your company has a match, fund that 401K up to the match if you can and do it asap.