Best Engine?
Hmm, several possibilities.
The one(s) attached to the airplane you're currently flying of course. (they can hear your thoughts, so be nice)
An airframe manufacturer (or airline when given the option) may select engines for a given airplane type based upon several performance specifications. Like any other set of design considerations, there are minimum standards (many of them specified by regulation) to be met or exceeded and there are desired characteristics. As always, the optimal compromise between the factors to be considered is the somewhat illusive goal of the selection process.
A complete list of specifications and other priorities to be considered might require several pages. For a non airline use airframe builder, it may be as simple as installing the engine that best meets the design performance specifications established to meet customer expectations.
Engine selection for an airline fleet is anything but simple. With an airline the bottom line IS the bottom line. Accordingly the question might become: Which of the available engines will best allow us to achieve the financial goals we've established for ourselves? Since those goals are established in the executive wing, the matrix of competing priorities may leave the line pilots and maintenance folks with something they are less than happy with while simultaneously pleasing the CEO and bean-counting cronies to no end.
Therefore, the answer at the top of this post is good as any!
Or you can just choose your brand and support it no matter what.
Put your trust in God and Pratt & Whitney. 