I am figuring out what is best for the user and ease of experience. Should we give them pre selected amounts or let them enter in whatever amount they desire?
Providing a list of suggested donation amounts is not really intended to make things easier for the user. It is a tactic with the goal of increasing donations by influencing users' opinions on what a "reasonable" donation is. For this to work, appropriate amounts have to be suggested. The wrong suggestions could turn away users (by setting the bar too high) or reduce donation size (if you suggest less than what they would have given anyway).
- This is a tried and true tactic for increasing donations.
- The amounts that work will depend on your cause and users. Testing is needed. This is a good scenario for A/B testing.
- Always also provide a free text box to enable people who want to give more to do so. You would not want someone to be prevented from giving a larger donation because it isn't possible on the site.
Almost definitely DO NOT fill it in for them if there is an option to donate nothing. This would likely result in having to reverse a lot of donations. Seeing as this looks like is a required field, if it is pre-filled the form could submit without the user ever noticing how much they are donating. Leaving it blank lets them explicitly choose.
A suggestion might be for you to use radio buttons instead of a dropdown/combo box if there are only a few tiers of pledges, and depending on the purpose of the form.
This is a similar question to a famous UX question about tipping in taxis.
It's better to allow the user to select, why? because some users would have a hard time deciding how much they want to donate. The downside of giving them a selection is that if you give the user 3 options of small medium and large, most of them would select the middle option regardless of how high or low it is. There's a guilt and feel good factor playing in here.
Came across this. you might want to check it out. https://trybravo.com/
you can also checkout how various kick-starter projects provide backing options.