What zorn said. There aren't ever any Tango fares into or out of the USA. Tango Plus fares are priced where Tango would be domestically, because to the best of my knowledge every major US airline provides 100% mileage credit for all travel within the USA and between the US and Canada.

EWR vs. LGA: EWR is one of my least favorite places on earth, right up there with LAX. I haven't tried LGA but could it really be worse? :P