Spanish is my mother tongue. Italian is somewhat easy to understand, especially in spoken form, but it can sometimes get real tricky. On the other hand, written Portuguese is an absolute piece of cake. To me, it looks like funny Spanish with a lot of misspellings and weird word order :) As far as spoken Portuguese, it is easy to understand Brazilians, but not so Portuguese, because their accent is a lot more nasal and they do not articulate. In general, it is easier for a native Portuguese speaker (whether Brazilian or Portuguese) to understand spoken Spanish than the other way around.
Besides Spanish, I learned English AND French simultaneously as a very young boy, and I am absolutely fluent in those three languages. No foreign accent, particularly in French. Since my primary school education was in Spanish and my high school was in French, I count and do basic arithmetic in Spanish, but solve more sophisticated math questions, such as second degree equations and square roots, in French. Funny how the brain works.