The list of creatures that dismember always kills and spatial always doesn't in modern is somewhat short
Sorry, but no. Other than the targets you already spoke of, let’s look at: Knight of the Reliquary, Reality Smasher, pumped Spell Queller, pumped Archbound Ravager (or anything pumped in Affinity, really). Small Death’s Shadow and Tarmogoyf. Grim Flayer, Voice of Resurgence tokens, Champion of the Parish (most of the time), or pumped Mantis Rider. Pumped Tireless Tracker and Scavenging Ooze. Unflipped Thing in the Ice. Celestial Colonnade and Restoration Angel. And much, much more.
There is no contest. Even because turn ONE removal is always better than turn two, or simply spending one mana versus two in some crucial turns. Spatial is good, but only as a complement of Dismember (thus, in the sideboard).