Regardless of views on the type/quality of PwC's work, the internship programme is centrally determined and is relatively standardised.
The internship will look good on your CV, but the work you get will be not much different from the work that an audit or a tax or a corp finance intern does, and will not be on the project's "critical path".
Smaller firms such as CVA have less reserve bench strength so are more likely to have to use interns on client projects. The absence of a centrally controlled programme means a project manager who has appropriate work and is short-handed will make good use of interns. However, the absence of programme control means you're just as likely to get a project manager who doesn't want to p*ss his/her client off by diluting the standard of staff on the project.