I don't think it really matters which language you pick, if your goal is to learn object-oriented techniques. The important thing is to learn the concepts and to start thinking in terms of them. Implementing object-oriented designs in LabVIEW is very different than text based languages because the semantics of the language are so different. However, the underlying concepts are the same and can be fairly easily applied. The important thing is to get yourself thinking in object-oriented terms. This is a transition that usually occurs somewhere between one and three months after you start learning and using an object-oriented language.
Good luck with whatever you decide.