Reputation comes first
Direct comparison Simtech - Sky4u
A) reputation: Simtech was founded in 2004, Sky4u much later. Business is running, expanding constantly since then.
B) quality: simulators and instructors of simtech well known for top quality. Most Simtech students found an airline job and flying all around the world.
C) costs: training at Simtech is worth every penny even if little more expensive than Sky4u. The biggest extra is the wide range of airline contacts, that you can write to or call for further information on screemings. Not to forget the better and newer simulators.
The winner is clear: Simtech