Menstrual Cup....Help!

Stephanie
I've been debating trying out a menstrual cup. I've used tampons for about 15 years now so this should be interesting. I'm trying to get as much info as I can before I purchase one so I'm relying on you guys!
How do you determine what size to buy?
Is it somewhat difficult to use in the 
beginning but gets easier with practice?
Best brands?
Good experiences?
Bad experiences? 
Thanks ladies! 😘