Skype or tango?
I use Skype, but that's mainly because a lot of the people I talk to already have a Skype account, and they use it on their phone and/or computer. Next to none of them use Tango, so it's one less app/account to worry with.
Current lineup: Note 3, iPhone 5S, Note 10.1 2014
Previous smartphones: Note 2, Galaxy S3, One X, RAZR MAXX, Galaxy Nexus, Rezound, Note, iPhone 4S, Bionic, Stratosphere, Charge, Vitality, Incredible 2, Thunderbolt, Palm Pixi Plus, Droid 3, Fascinate, Incredible, Droid Pro, Droid 2 Global, Droid X, Droid, Treo Pro, Touch Pro 2, Touch Pro, Q9m, XV6800, XV6900
Previous tablets: iPad Mini, Transformer TF300, Evo View, Transformer Prime, Transformer TF101, Thrive, gTablet