I bought my first Rolex in 1983 (an 18k President), sold it in 2003, and began collecting Omegas.
During the past six years, I have owned at least one example of each of the Omega lines including a Museum piece. Quality and workmanship are comparable between Omega and Rolex. I would give Rolex the edge for perceived value (marketing) but Omega wins out for actual value.
As for being lifetime watches, my Omega "bumper" automatic is almost 60 years old and although not COSC, is far more accurate than my President ever was. Likewise with my 44 year old Speedmaster Professional. Both old-timers are never more than 2sec/day off. And Omega still maintains parts for them if need be.
As for the modern Omegas, the latest and greatest is the "in-house" cal. 8500 built from the ground up to incorporate the co-axial escapement. Theoretically this new technology eliminates friction providing better accuracy and longer intervals between servicing.
At the outset, Omega incorporated the co-axial escapement into existing movements, most notably the workhorse cal. 1120. This movement with the co-axial added was renamed the cal. 2500 and was the standard movement in the Aqua Terra (version 1) and Planet Ocean lines.
I currently own two Omegas with non co-axial cal. 1120 movements, the Seamaster Professional 2254.50 and 2255.80, both divers. I also own two cal. 2500 co-axial Aqua Terras, models 2803.34 and 2504.50. The accuracy of all four is about the same as my Explorer II, less than 2sec/day. As to whether the service interval of the co-axial watches will extend beyond the standard of five years, only time will tell.
The Planet Ocean is thicker than the Sub and the EXPII because of the increased water resistance of 600m/2000ft. The Seamaster Professionals and Bond watches with WR of 300m/1000ft are similar in thickness to the Sub and EXPII.
To me, it would be unfair to compare the Sub to the Planet Ocean. The Planet Ocean contains the co-axial technology and has twice the WR rating. The Sub is more comparable to the Seamaster Professional models with the cal. 1120 movements and the same WR rating. In any objective review and testing, the Omega SMP and Rolex Sub are about as equal as any two watches can get.
Now let us compare the respective costs of the two watches. The MSRP of the Sub Date is $5850 while the MSRP of the Omega is $2300. Discounts vary but it is not unusual to find Omega watches for as much as 30% off of MSRP. (Unfortunately the cal. 1120 Seamasters have been discontinued as Omega is incorporating the co-axial escapement into all lines. This technology has added approximately $1000 to the MSRPs; i.e., the MSRP of the new co-axial black Bond is $3400.)
But look at the MSRP of the Sub versus the Planet Ocean. The MSRP of the 42mm PO, $3550, is considerably less than the Sub. With discounting, you could buy two POs for the cost of one Sub.
Last year I purchased a new Explorer II to fill the GMT niche in my collection. I wanted a classic, quality watch and I selected the EXPII. Yes, even buying it gray market at a 20% discount, it was still overpriced. Nothing about it is really "state of the art" but it is suitable for its intended purpose. But if Omega offered a similar piece, I would not have a Rolex in my collection.
Bottom line: Omega and Rolex are good (not great) watches but Omega represents the better value.
(And invariably at this point, someone will at this point bring up the resale value of Rolex. That is a topic for another discussion but having owned 80+ Omegas, I have the data to show that Omega's resale value is on par with Rolex.)
P.S.: Please excuse the long post.