I liked Swapnote a lot better. Swapdoodle tries hard to replicate what Swapnote did quite well, but having to pay for the extra features are a big turnoff for me. The fact they are keeping Swapnote alive on its deathbed to send notes over StreetPass instead of bringing that over to Swapdoodle was a very much a missed opportunity.
I haven't tried swapdoodle but I used swapnote SO much!! I loved it! Sending weird drawings to my friends was my life. xD Then Nintendo took away spotpass for it so then it became virtually worthless cause I don't have that many people close to me playing 3DSs for streetpass to be worth it. Sucked very much. After that, I saw this and decided to skip it, thinking it was the same thing.
I downloaded it, but I don't know anyone else who uses it. It also seems silly to have to pay for things like extra paper designs and different colored pens.
I used swapnote a lot during 2012-2013 but I don't have anyone from my old roster plus my new friend roster isn'the very active so I don't really use it anymore