Transferring Money from Roth 401k to Roth IRA, when does it make sense?

[Swat]

I am a current medical resident and soon to be attending. My wife worked throughout residency but stopped after the birth of our son. She has been investing in her company retirement plan. They have a Roth option so we have contributed all money to their Roth 403b (with me in lower earning years as a resident). We will be moving and not going back to her current employer, and we’re not sure when she will resume working again (and if she does, likely will be part time). Her Roth 403b totaling ~$50k is currently at Fidelity in two excellent Institutional Premium funds, the S&P 500 (FXAIX, ER 0.015) and International Index (FSPSX, ER 0.045). However, her Roth IRA, and the rest of our money (my Roth, Taxable Account) are all at Vanguard. I’m trying to decide whether it makes sense to keep the money at Fidelity in her Roth 403b but not be able to make other contributions vs rolling it over to Roth IRA at Vanguard? Here are the ideas I’m wrestling with:
-ER at Fidelity Institutional Plus Shares are better than Vanguard Admiral Shares: favor Fidelity Roth 403b
-ER between Institutional Plus and Admiral shares is not THAT MUCH DIFFERENT (we’re not talking active vs passive funds for instance): favor Vanguard Roth IRA
-Inability to contribute further into the account: favor Vanguard Roth IRA
-All of our other money is at Vanguard: favor Vanguard Roth IRA
-Prefer TSM fund vs S&P500 (albeit minor difference): favor Vanguard Roth IRA
-Moderate amount of money in the account (50k is not incredibly small but also not huge either): tie
-Her future employer (whenever that may be) could use Fidelity for their workplace retirement account: Favor Fidelity Roth 403b

I would appreciate any and all thoughts.

[Proud Foot]

For $50k the difference in ER will be minimal per year. The difference will come in whether the 403b charges any additional fees, particularly for former employees. You might also look into whether her plan allows her to stay in if she is no longer an employee and how long before she has to have it transferred.

As far as the rest of your list:
Contributions - IMO should not make a difference. You can open up a Roth IRA at Vanguard without rolling over the Roth 403b
Other Money at Vanguard/Investment choices - Makes sense to move it to Vanguard if you want all your accounts at the same place and they offer the investment options you want.
Future Employer - Should not matter. No retirement plan is exactly the same so even if it was at Fidelity they may not offer the same investment options with the same ER's. If the new employer does you should be able to roll her Roth into the new employer's plan.