Hey!
Congratulations on the vacation scheme!
I wouldn't say that there is necessarily harder departments for a vacation scheme. In my experience, the difficult usually depends more on the specific task and supervisor, rather than the practice area itself. Whilst I did notice that some teams were busier during vacation schemes that I completed, so the candidates in those teams usually ended up staying slightly later, supervisors generally know that you'll have limited experience and will try to set work that is appropriate for that level.
If you don't have experience in any of the teams, I would simply choose the one that sounds most interesting to you or that you are most curious to learn about! One of the purposes of the scheme is to explore different areas of practice, so firms don't expect you to already have knowledge of the department you choose. I also would try not to be disappointed if you are placed in a department that you didn't have a pre-existing interest in! During my
Stephenson Harwood vacation scheme, I was in Regulatory Litigation for part of the scheme, and I had convinced myself I was
not a litigious person in any way. However, I really enjoyed my time in the team and found the work super interesting - so you might be surprised!