Brand comparisons usually run on opinion. This one runs on settled transactions: 1,383 recorded sales of Omega and 81 of Grand Seiko, all in US dollars so the figures are directly comparable.
What each one actually costs
The median Omega result is $3,120. The median Grand Seiko result is $4,620. On typical examples, Grand Seiko carries roughly 1.5 times the price of Omega at auction.
Half of all Omega sales land between $1,680 and $6,000. For Grand Seiko the middle half runs $3,355 to $8,456.
Which one surprises the specialists
32% of Omega lots beat their high estimate, against 27% for Grand Seiko. The two are closely matched, which suggests both are priced with similar confidence.
Breadth of the record
Our archive covers 407 distinct Omega references and 63 for Grand Seiko, with results going back to 2001 and 2012 respectively. The top recorded result is $324,500 for Omega and $78,740 for Grand Seiko.
What this does not tell you
A median is not a verdict. These brands overlap heavily at the edges, and a well chosen example of the cheaper one will outrun a poor example of the dearer one. Condition, completeness and model matter more than the badge on the dial.