Feeding any pet will obviously do a lot of good for them. Feeding any pet is great of course.
I don't know if Louis ever stops missing with his gun shot someone else will have to answer that

As long as you're willing to feed/scroll/spend IM then any pet should end up being rather good

.........

Before I even read your points I said Clive and you overall had more positives for him

I get what you mean by Louis is cool but I can't see him ever being RB for us plus he is limited to using a gun like you mentioned...

Same with Joan (I personally like her too) but then you would probably end up getting her to 180 and then nothing because she does not have RB too

Clive however can RB so he just gets a whole bunch more stat points and he is pretty strong if you scroll him early and can hit more than 1 enemy at once. And honestly I think he is 'cooler' than Louis (just thought I'd chuck that in xD it's my opinion though)

In the end up to you but I would go with Clive out of your three options