Cory, there are very few reasons to not rollover your 401(k) into an IRA but here is an article I wrote about all the options you have: http://nicholasolesen.squarespace.com/blog/wednesdays-qa-with-nicholas-what-should-i-do-with-my-old-401.html
Yes. Most 401k plans have limited investment options and all of them have embedded fees and expenses which can be reduced or eliminated through a self-directed rollover IRA. One reason that you might want to keep the 401k plan is if you can maintain a loan option, but most plans terminate this option if you are no longer an employee. Some 401k plans are so expensive and have such a poor investment lineup that almost any alternative would be superior. Whether you choose to work with an advisor or manage your roll over account on a self-directed basis, be sure to align your portfolio risk with your long term needs and goals, diversify your exposure by asset class and style, and watch the expense ratios on your managed investments. Best of luck!
Cory, as the others here have indicated, you will have more control and better investment options available to you in an IRA, compared to your 401k, in most cases. Before you do, you will want to ensure that an IRA has the same legal protections as a 401k does in your state. Most states offer the same protection from creditors, etc., but some do not. If yours does not, then you should consider that before moving.
As for investment options, I highly recommend a globally diversified, balanced portfolio of high quality funds that will help give you both offense and defense. If you would like more information, check out the book by Dr. Craig Israelsen called, "7Twelve: A Diversified Investment Portfolio with a Plan" on Amazon. This is a solid strategy. If you don't want to do it yourself, then you could try to find an advisor in your area that uses this strategy. Our firm can also help you in this regard if you don't want to start from scratch, as this is the same type of investment strategy we use, with a few extras. Feel free to reach out if you like. We can be reached at 303-422-7351.
Yes, in the vast majority of cases you should have access to a wider variety of funds and probably a more flexible approach. Take care as to what you roll into. It needs to be an IRA but within the IRA you might find a number of options from stocks and bonds to mutual funds to annuity products. The key is to know exactly what your funds will be invested into within the IRA.