This is an interesting but complex question. In favourable circumstances I believe that research skills are better fostered within a group project. A group project will in general allow more interesting and more complex problems to be investigated. Research skills require that ideas be formed, questioned and revised. A small group project can provide a suitable vehicle for individuals to form, exchange, defend and modify ideas and is likely to result in consideration of a wider range of concepts. Working in such groups can also be enjoyable and motivating and help to encourage perseverance.
However, in practice, there are a number of potential problems associated with group work. In particular, any discordance that arises is likely to reduce both motivation and learning. Often people feel that other members of the group are not ‘pulling their weight’ or a group may be controlled by a dominating individual. Both these problems can be guarded against when the roles and tasks required from individuals are made clear at the on-set. It is also found that intragroup cohesion is helped where an element of intergroup completion is present.
Group projects also create greater difficulty with assessment than do individual projects. It is therefore important that details of any accompanying assessment are made clear to students at the start of group projects.