You have three choices for the funds in your old 401(k) plan. The two you mentioned (leaving it where it is or rolling it over to your new employer) and third, rolling it over to an IRA. The best option for you would depend on several different factors, but generally . . . .
Focusing on debt payoff can cost you hundreds of thousands of dollars. Debt payoff strategies abound on the internet, and many mainstream financial gurus have built an empire on the common-sense approach to focus your financial efforts first on paying off your debt. The math, however, doesn’t work out in their favor.
The Stock Brokerage and Insurance Industries are fighting hard against the Department of Labor's Fiduciary Rule, which would require their advisers to put their client's interests first and disclose conflicts of interest. The industries got the 5th Circuit Court to agree that, unlike Registered Investment Advisers, stock brokers and insurnce agent are just salespeople
The DOL Fiduciary rule is now in force, but there is a loophole for commissioned advisers which can allow them to maintain their current compensation model. Make sure you understand the Best Interest Contract Exemption and the implications it has on potential conflicts of interest which could influence the investment advice you recieve.
Between the wide range of meaningless job titles and the alphabet soup of certifications and designations, it's easy for an advisor to hide how they truly do business. One thing an adviser can't hide, however, is how they're licensed. Knowing the license will tell you what they can advise on, how they are compensated, and whether they are fiduciaries.