Unless you have some form of discard recovery, I think Pokémon Communication would be the better choice. I would only use it if you have the sufficient energy for the card that you choose from your deck so that you can play it ASAP before your opponent readies their bench. If you have a way to recover cards from your discard pile, then I say Ultra Ball is better.
Location: In your fridge, eating your fruit salad. ;)
Nine out of ten times, I prefer Ultra Ball. There's a higher likelihood that you'll have two spare cards to discard than a Pokemon that you can't use at the time (usually happens only if you have two copies in your hand). Often times you can afford to discard draw supporters like Cheren, Juniper, etc and/or an energy or two if it lets you search for the Pokemon you need right that moment.
Pokemon Communication may be better in a speed deck with lots of strong basics, but I wouldn't find it as useful in an evolution heavy deck. It's basically the same as the BS Pokemon Trader, but thanks to Ultra Ball there's a more viable option for that. However in a deck with strong basics of varying types, Communication might let you get to the perfect Pokemon for the situation without discarding.
you may also wish to consider Master Ball, an Ace Spec that lets you search for any Pokemon without having to swap or discard. It can be an alternative to Computer Search, especially if you have 3-4 copies of Skyla in your deck.
Ultra ball is generally better than Poke-communication. Most decks use very little Pokemon with a high number of trainers/supporters/stadiums so always having a Pokemon to put back into your deck to search for another one is not likely.
Ultra ball also has synergy with some decks which need energy in the discard to use effects such as Dark patch for Darkrai decks and Eeletrik's Ability for lightning decks.
Most of the time the supporter you play will refresh your hand anyway, so discarding some resources is not always a bad idea.
So if you run heavy Pokemon line up decks, then communication may not be a bad idea, but in the competitive tournament play most people use Ultra Ball, Level Ball and Heavy ball along with Skyla and Computer Search.