I have trouble understanding Mexican. I find Castillan much easier. And I have had short conversations with a girl I work with who speaks Argentinian (Although she laughs at my accent. And it seems that a 17 year old girl doesn't expect to be addressed in the Ud. conjugation, I threw her off when I started speaking what passes for Spanish for me). Cuban relaxes me to the point where I want to go to sleep, I'm not sure why that is.
Honestly, I'd be thrown off too if I was addressed with Ud. by someone older than me. Usted is typically used for elders and strangers around your age.
Speaking of which, try to understand Catalan.
I don't know anything about Portuguese, but the Spanish people I know say that it sounds like they SHOULD understand it, but don't. (I use "Spanish" to mean people who speak a dialect of Spanish, not specifically Spaniards)
I can confirm that, myself.
Speaking of Spanish, the distinct lack of an n with tilde on my German keyboard irks me. I hardly ever use it, but still. (Yes, I can switch it to Spanish. It's just not the same.)