Debating performance or failure rates is always a can of worms on the internet. Here are the differences as objectively as I can describe:

Shifting - Ultegra has the "lighter" shift action for the rear derailleur, going to harder gears (ie: 12T > 11T). The paddle requires force comparable to pressing the key on a laptop, whereas Sram's paddle needs noticeably more. Also, Sram's shifting indexing mechanism is louder - a CLACK sound as opposed to Shimano's click.

Lever adjustment- Due to the STI mechanism, Ultegra's levers cannot be adjusted individually. If you want the shift paddle moved in, the brake lever must come in also. Force has an indexed adjustment for the shift lever (3 positions iirc), and "infinite" brake lever adjustment via a grub screw.

Brake Lever - Shimano's big lever is responsible for both shifting and braking, and Sram's is a dedicated braking lever. It is possible for the Ultegra lever to swing laterally while pulling the lever for braking.

IMO, the systems' only significant differences are in weight and shift mechanism. That said, the only disadvantage I've found with Sram (Force) is shifting to an easier gear in the rear when I needed it going uphill. The shift takes a bit longer because the lever has to move inboard farther (to initiate the downshift). Had I been on a Shimano system, the downshift would have occurred as quickly as I could push the brake lever in.