The rule I follow is to pronounce it the way the locals mispronounce it. Works everywhere I travel. "Gua" at the beginning of a word can be pronounced at least three different ways and sometimes varies regionally for the same word. I've mostly heard Guanajuato pronounced with a silent G as the UA diphthong "wah", but occasionally with a hint of hard G.
Now X is a letter I hear pronounced with more variants than I can count. Largely due to the phonetics of indigenous languages like Nahuatl. MikeMike, how do the Veracruzanos pronounce our favorite convenience store, OXXO? Maybe not like the Chilangos do.
Someone want to take a shot at Cuautitlán-Izcalli?? Spanish phonetics don't apply to this one either.
"You don't take photos for yourself, you take them for the old man you will become - if you are lucky." - Falang
"As long as there's a horizon and I can see it, then I want to know what's there, mentally, physically and visually" - rtwpaul