Dogecoin is rank#12 and Shiba Inu is rank#13 by coinmarketcap as of December 22, 2021. A very close fight. On a question of which is better for investment? For me, both of them are good. But again before putting your money you need to do some research about them so that your decision will be well guided.
Personally, I see this more in terms of lifespan and also more on the important things that exist in both of them where Shiba Inu tokens have not developed their wallets because they are still very new in the cryptocurrency space while for Dogecoin it is the oldest memecoin that has been around for a very long time in cryptocurrencies with some good updates and the rankings that happened to both of them are also not new for now because it's been almost a month they are both ranked 12th and 13th in coinmarketcap