I like both Lapis as well as Cobalt . Lapis is more traditional and was quite popular with 996 cars and earlier boxter . Cobalt came to the scene later on and looks amazing on a Turbo with ceramic (or Brembo) yellow caliper brakes. Lapis seems somewhat lighter than midnight and Cobalt somewhat darker than Aqua .
There is one shade of blue that differs from all of them --Mexico Blue . I think it would look GORGEOUS on a GT3 and even would make a 997.2 completely unique.
Here's a clip of it on a Cayman S .