If I'm considering FIRE in the near future it seems like it would make more sense to get that money into a Rollover IRA so that I would have the option to do the Roth conversion to provision for planning it into a Roth ladder.
Just prior to retirement if you really need to increase your Roth balance, it's just as good (often better) to switch new contributions to Roth than it is to convert existing funds. The contributions can be withdrawn for free at any time, while you have to wait five years to withdraw conversions for free. Also if you must do conversions, look into the option of an in-plan Roth conversion within your 401(k). Many plans offer this option.
Greenstache's comments above about comparing the investment options between your existing 401(k), new 401(k), and IRA are solid. Some 401(k)s, especially at bigger companies, offer institutional index funds with lower expenses than you'll be able to get in an IRA. Other 401(k)s have pretty high-fee options. If that applies to you that might nudge you in the direction of an IRA rollover.
If your income is high enough (or might become high enough) that backdoor Roth IRA contributions might look like a good idea, you'll want to keep pre-tax money out of your IRA to leave the backdoor Roth option available to you.
If you think you might leave your new job sometime between the year you turn 55 and the year you turn 59½, you'll be able to make penalty-free withdrawals from that 401(k) but not your IRA.
Those are the main considerations I can think of. In many situations it doesn't really matter too much which option you choose.