I use the Playtex insulated tumblers and do not have any leaking issues. We've had out current ones for at least 6-7 months and I put them in the dishwasher every time they are used, about once every 2-3 days since we have 4 of them.
The best one I've found I believe is by Gerby. They are hard plastic and shaped like an hour glass. They have a removable valve. I've never had problems with them leaking. I've had mine for like two years now and not one problem our ot them. I belive they are $5-6 a piece but worth the investment.
Ok so I looked at what we use for alexis - are Gerber-brand (they are hourglass shaped with different color tops) - you can find them at target(that's where we got them). FYI I don't like the nuby - those i've found to leak - bad.. they toppers are plastic so if you get any separation, that's it for them!!