I know that there are existing threads about buying paper gold, but I wanted my own.

Plus, I wasn't sure if there are different recommendations based on whether you're putting it in a taxable account, a Roth IRA, or a tax-deferred account like a 401k. Normally you can't buy gold in employer-administered 401k accounts, but a while back I had a side business (still do, as far as I'm concerned, but haven't reported any income/losses on it in several years). When my wife and I each left our jobs at the time, we rolled over our employer-provided 401k accounts to these accounts. Initially, they were administered by Vanguard, but later converted to TD Ameritrade. So in these TD Ameritrade accounts I can purchase any stock I want (at one point I had the money invested in PRPFX).
Anyway, so I've got that TD Ameritrade 401k account. We've also got our Vanguard Roth IRA accounts. I'm not sure what I can/can't invest in with that Vanguard Roth IRA account. If someone can advise on that, that would be great.
For the TD Ameritrade 401k accounts, what would be your recommendation for a paper gold fund? I've seen a lot of different recommendations in this forum, but I simply can't understand a lot of the finer details, so please provide answers in a dumbed-down manner.