If you are happy with the investment choices available at the new company, it will be less hassle to roll over to that company's plan. If you roll it into an IRA, you will have to take care of two accounts, but you will be able to make all your own investment choices. Typically, the funds available in small-company 401(k)s are mild to moderate rip-offs, and you will likely pay less in expenses by opening an IRA with Vanguard, Schwab, Fidelity, etc. However, you cannot borrow against an IRA, which might be important to you.
Whichever rollover choice you make, the two key things to remember are: Roll it over, don't cash it out! So many people cash out even though they end up paying that 10% penalty, which means they never should have put it in the 401(k) in the first place. Second, insist that the funds be transferred by wire from the old to the new account. If you get a physical check, there are extremely strict rules about how it must be deposited which could lead to a huge penalty, and sometimes there are tax withholding problems as well. Just pay for the wire transfer, it's cheap insurance.
Walt (also not giving investment or tax advice)