From my experience the best comes from a combination of both. Everyone think separately and come up with your own solutions, then meet as a group and everyone g

From my experience the best comes from a combination of both. Everyone think separately and come up with your own solutions, then meet as a group and everyone goes over their ideas, then go one by one and list the pros and cons of each solution. Typically you can eliminate half right off the bat. Then you go through each of the remaining ones and brainstorm how you can tweak it to maximize the pros and minimize the cons. Sometimes you can't make any changes and sometimes you end up combining different parts of different solutions into one. Note that this will only work in small groups, like 3-5 people or so.