We had a hard time trying to find a sippy cup that was easy to suck because of DD didn't have the strength to suck real hard. After buying at least 1 of every cup on the market (or maybe it just seemed like it

) We finally found the Nuby brand at
Walmart. She tried it, loved it, never wanted her bottle again! It has a really flexible spout and no extra vents to wash. Give those a try!