My general advice is as follows:
* If your new 401(k) has institutional-class index funds with lower expense ratios than you can get in an individual account, put the money in the new 401(k).
* Otherwise, if your old 403(b) has institutional-class index funds with lower expense ratios than you can get in an individual account, leave the money where it is.
* Otherwise, roll the money into a Vanguard IRA.