Similarities:

You are considering five automatic winding
: chronographs, all of whom have a date function.
: All have (I believe) sapphire crystals.
: Four of the five have 100M water resistance.
: Four of the five have a tachymeter scale.
: Three of the five have the same base movement, the ETA/Valjoux
: 7750.
: Three of the five have the typical 7750 dial layout of 12-9-6
: positions.
: Three of the five (the Omegas) are
: chronometers -- tested and certified for
: accuracy.

Differences:

Check to ensure the Oris has a
: sapphire crystal.
: The Oris has 30M water resistance.
: The Oris lacks a tachymeter scale.
: The Omega coaxial has a Frederic Piguet chronograph movement with a
: coaxial escapement, which is a significantly better timekeeper.
: The longer numbered Omega also has a Frederic Piquet chronograph
: movement with a traditional escapement.
: These two watches have the more traditional and balanced
: "tricompax" dial of 3-6-9 positions.
: The TAG and Oris are not chronometers, which means not only that
: they were not tested, but that a lower grade and less finished
: 7750 movement from ETA was used.

Brand comments:

Omega
: finishes their movements to a high degree and alters ETA
: movements with their own improved winding system.
: Note the number of watches with exhibition back in the Omega
: collection; there is no difference in the movement used in a
: closed back watch and the exhibition back watch (excepting a
: nylon part in a manual chronograph movement you are not
: considering).
: Omega uses F. Piguet high grade movements (F. Piguet movements are
: used extensively in far more expensive watches than Omega).
: All Omega watches have a high level of fit and finish to the case
: and bracelet.

: TAG makes fine watches, but few are well finished, and it is
: somewhat rare to see exhibition backs.
: Where TAG has features comparable to Omega, they are nearly
: equivalent in quality (chronometer vs. chronometer), but the
: finish details may be slightly less.

: Oris is simply a cheaper alternative, using lower (often lowest)
: grade versions of the same movements.
: The fit and finish are not comparable, particularly in the watch
: face.

Closing:

However, a mechanical watch is a bit of a
: passion. A quartz watch will keep better time and most won't
: know the difference.
: It is about how you feel wearing the watch.

: Try the alternatives (or a close equivalent) on and see it on your
: wrist. Internet photos are no substitute for wrist time.
: If possible, compare the alternatives side by side.

: Good luck in your search.

: Sam

Sam:

Thanks a bunch. You have helped a lot.

Nails