Maya PLE is the full version of Maya Complete with just the watermark. If you want to learn maya, then PLE Is the way to go. XSI EXP is also similar. Heres a page that compares the two (biased towards XSI though)
https://www.softimage.com/products/exp/v3/head_to_head/

I haven't tried EXP because my LCD monitor cant go up beyond 1024 x 768 res , which is a requirement for EXP. It actually turns out they have layouts for 1024 x 768.
I might try it out once Half Life 2 comes out.