My sister flew PLUNA to Punta del Este because their advertised fare was only 20% higher than Buquebus. Then the airline started hitting her with surprise fees: boarding fees, luggage fees - there was a fee even for her carry-on, and other assorted expenses. She ended up paying almost twice what Buquebus charges, and swore never to fly PLUNA again.
That airline is poorly run - it was hard to get anyone to answer the phone in Punta del Este, and she had to go all the way to Maldonado to pay a fee, as the Peninsula office was "not authorized" to take payments.
I've been advised to fly LAN whenever possible - it is supposed to be the best regional airline.
I've been advised to fly LAN whenever possible - Aerolineas is in the middle of dispute between Spanish and government interests, and prone to wildcat strikes.