Teaching Molly to use a sippy cup

Well, we have been trying to teach Molly to use a sippy cup the last little while. I tried when she was first 6 months old, but that failed. We had the AVENT trainer cup, and thought it would work well since she used the AVENT bottle system. Well, she really has struggled with it. So out of desperation, I picked up a Gerber sippy cup to try. Well, she has really picked up on drinking from it much better than the other. I haven't tried the AVENT trainer cup again since we tried the Gerber. I imagine once she gets the hang of it, then she should be able to drink from both. She will be 8 months old on the 11th!!! I can't believe it.