Should an IRA or 401k be transferred into a trust?

It is definitely not a good idea!  If you put your IRA or other qualified retirement account into your Living Trust, the IRS will consider it as a distribution and you will be taxed on the entire amount immediately.  There are other ways to do what I’m sure you want, i.e. control the timing of the distribution of the IRA after your death.  One way is to create a separate special trust to hold only the IRA, and there are others also.  The easiest solution is to make your Trust the beneficiary of your IRA.