Colombian Spanish is widely considered to be the most neutral, "unaccented" Spanish and the one that is most easily understood by non-native Spanish speakers - especially those who are just beginning to learn Spanish.
Educated, native Spanish speakers will have no problem understanding Spanish in any other country except maybe with street Spanish spoken by uneducated speakers.
I remember when I lived in Puerto Rico I was at a bar one time with a Peruvian friend of mine. Some Puerto Ricans next to us were having an animated conversation. I asked him what they were saying. He said he didn't have a clue - could only understand a couple words here and there because of the heavy accent.