Which bond fund to contribute to in my Roth IRA?

Currently only have 2.5% in bonds between my Roth IRA and 457(b). I'm still young (36) and a ways out from retirement but I do want to add a bit more to bonds. Planning on allocating ~5% of my portfolio to bonds. Which bond would you recommend investing in for my Roth IRA? BND? BNDX? VGLT? VGIT? Open to other suggestions as well, those just seemed to pop up the most when researching this.