Per head cost or Consumption bar??

Never ever do consumption bar because you will be charged everytime someone gets a new glass after taking 2 sips and there is no oversight with the final bill.

Definitely per head! Say a drink is $8. 4 drinks in 4 hours, which is completely reasonable, and your're already at your open bar cost. Heavy drinkers will drink more than 4 drinks. Also factor in people who get a drink, put it down, never come back to it, and just go get a new drink. Consumption bars almost always end up being more expensive unless you have light drinkers.

1000% don't do a consumption bar, one of my family members offered to pay for a consumption bar at her son's wedding and it came out to like $140/person.

I would definitely do per head. Consumption bars tend to be way more expensive in the end because at weddings, many people get a new drink before finishing their current drink (or they get up to dance and forget about their drink). And $35 for 5 hours is an absolutely amazing deal!

In your case, I'd absolutely go per head. I'm doing a consumption bar because it will end up being cheaper in my case. We're just doing beer and wine and are supplying the wine so we're really only paying for the beer. Our beer drinkers are also people who will hold onto their beer until it's done, so I'm not worried about them taking a couple sips and forgetting where they put it. But with 50 moderate-heavy drinkers, and especially if it's a full bar, per head will end up costing you less.