Dragon Shield's standard sleeve runs noticeably thicker than Ultra Pro's, around 90 microns per wall against Ultra Pro's thinner stock. That extra plastic means a snugger fit that holds a card still inside a toploader, at a price that's usually a few cents more per sleeve.
Where Dragon Shield wins
Fit and durability for cards that get handled or shuffled. The thicker wall shows less wear over time, and the snug fit reduces surface contact and rattle inside a toploader. It's the sleeve we reach for on anything going into long-term storage rather than straight to a mailer.
Where Ultra Pro wins
Price and availability at volume. Ultra Pro is the sleeve most shops stock by default, and for a bulk lot going straight into penny sleeves before sorting, the lower per-card cost adds up fast across a few thousand cards. Ultra Pro's Perfect Fit inner sleeves are also the standard pairing for double-sleeving before a rigid holder.
What this doesn't decide
Neither brand's standard sleeve is archival-rated on its own, and neither replaces a toploader for anything shipping or grading. A sleeve protects the surface from a toploader's rigid edge; it doesn't protect the card from bending or a corner ding by itself.
Shop Dragon Shield on Amazon → (paid link) Shop Ultra Pro on Amazon → (paid link)