I would let people choose tbh OP, charity giving is quite a personal thing, there are some I wouldn't donate to. I'd pick something small and local, for maximum impact. DP worked in finance for a large and well known charity a few years and the % that actually goes into projects from single donations by individuals (or adoptions and subscriptions etc) is fairly loe.
My best friend married last year and set up a Just Giving for a charity relating to a deceased family members illness, for her wedding, gave out cards with the charity pins on as favours and link to donate (which was also on the invite). Sadly almost all the pins were left on the tables at the end of the night still and it did upset her a bit. I think they had a handful of small token donations from immediate family and that was it (which also upset her as it was something in her mind related to the family member and felt to her that people didn't care about said family member. It put a real dampener on it, we had do a sweep of the abandoned pins and dispose of them.
Obviously people are free to donate or not (I obviously did, for her) and made a point of taking the pin- but I will say that it's a bit wasteful, the pins aren't really going to be worn or used or even kept (realistically, unless by people also close to the deceased). I would prefer just to donate.
Really not trying to be a downer OP honestly, just pointing out that on the day, if the charity you choose holds real meaning then there is scope for upset to you. Fingers crossed it would go the other way for you and your guests are nicer than hers were
. I did also see someone leave early with an unopened bottle of the table wine in hand, so there you go!