DCA into VOO or start position in VTI?

Curious which option makes more sense...DCA into VOO (cost basis currently is $421) or start position in VTI to diversify at current price, even though returns are essentially the same for each fund over long term.

Also, currently put $400/month into my account, so wondering if it makes more sense to just buy VTI right away each month or wait to purchase VOO every two months.