Be pro- #accessibility. So that screen readers don't end up spelling multiple-word hashtags out one letter at a time (please consider how frustrated you would be if this was your experience!) do this:

#UseInitialCapsInYourHashtags

aka

#WriteItInCamelCase

aka

#CapitalizeEachWord

So much easier for people not using screen readers to decipher too, especially when seeing it for the first time.