Stick with a closed-handed pull. An open handed pull/push is a telltale sign of a career rookie/semipro (with a handful of exceptions in the low pro ranks). In addition to making it harder to get lateral speed, an open-handed shot makes it a lot harder to hit consistent middles, control spray/square/cutback, etc. And it tends to telegraph more than a closed-handed grip.
Pro-master players basically use open-handed grips for 3 or maybe 4 things in real competition, depending on whether you count #4 as "real competition":
1. 5-bar shots where the speed the ball is hit matters a lot more than telegraphs, etc (almost all of them use open-handed shots at least part of the time on their hacks)
2. semi-open grips are used by guys like Gummeson on their stick passes (primarily for the stick wall)
3. Front-pins (Frederico's is open-handed, Swan's is closed-handed).
4. Bank shots, if they're used (Loffredo uses an open-handed grip for some pretty mean banks from goal, but he'll never use banks in real competition; Billy uses open-handed bank shots in goalie wars and occasionally if he's messing around in open events from goal).
I don't count the rollover as a typical open-handed grip but you could throw that in there if you're being pedantic. Some of the pull-kick shooters are open-handed as well, but there are only 3 pro-masters left shooting that as a primary that I know of (Thor Donovan: closed handed, Chris Dube: open-handed, Eric Dunn: Not sure if it's closed or open), I think all the (few) push-kickers are closed-handed. Some push shooters are open-handed as well but I think the handful of pros who shoot it do it closed-handed.