The major connections between dogecoin and Shiba Inu are the fact that they are both memes coins and have almost the same investors and supporters, and we have seen how the activities of these investors have affected the growth of both coins within this year one of those investors Is Elon Musk who tweets have turned the markets in different directions. Shiba Inu is presently up to almost 380% within the last few weeks and also saw dogecoin did a similar price hike in the previous month which have proven to the fact that both coins have been on a contesting mood in this altcoin season between Shiba Inu and dogecoin which is your most preferred choice for investment?
For me, I don't think there's any battle for supremacy what so ever between dogecoin and Shiba inu, personally, I see Shiba inu as the same dogecoin wine recycled in a new bottle, which means there's no difference between the two except for the bottle.
And like you said, if the investors of Shiba Inu are the same set of guys that invested in dogecoin, then there isn't really a competition between the two as it may well be possible they are just recycling money between the two meme coins.
And to your last question : ever since this whole meme craze started, I've never been moved to invest in any of them, even though I know this has lifted many lives from poverty, which is what we all pray for for ourselves, but then, I've never had this zeal of putting my money in a meme coin, I invest only in projects with proven legitimacy.