Most Contraries tend to run only moves that get boosted by Contrary, like Draco Meteor and V-Create, and most of the ones who have other moves tend to run recovery or anti-Shed rather than additional coverage. Consequently, anything bulky and neutral or resistant to those moves can run Unaware safely against them. For example, Unaware Cress can safely switch in to most Contraries as it only takes about 40% from Kyu-W's Draco Meteor and can then proceed to punish them. An Unaware sweeper, such as a Darm-Z I used to run in Gen V, can also just get in and set-up on the Contrary. Meanwhile, stuff like Flash Fire Aegilash and Togekiss wall most Contrary moves heavily and can stay in long enough to phaze or punish.
If you want an Unaware but are worried about it being dead weight in some games, then just make an Unaware sweeper. That way you can check other set-up sweepers, function against teams that lack them, and aren't scared if they Heart Swap or Imposter you.
Not to mention Contraries need momentum to get going in most cases, so if you can prevent that momentum you can deal with them without relying on Prankster/Unaware. And, if you can sleep or paralyze them, or burn for physical Contrary, they'll find it very hard to get any momentum.
As for Heart Swap vs Topsy, the former passes through Sub, the latter does not. The former lets you counter sweep or baton pass to a sweeper of your own while the latter pretty much ensures that they'll be shut down if they stay in. Heart Swapping Shell Smash is risky while Topsy-Turvying it is not. Remember there is other options though. Haze has a metric ton of PP if you need to constantly stop set-up sweepers and pretty much shuts down Baton Pass teams since PP stalling Haze takes a very long time. Perish Song will force the opponent to switch or die and, if they have Ingrain, guarantees a KO if they don't have an escape from their own self-trapping. Whirlwind, Dragon Tail, and Circle Throw shuffle them out, but is stopped by Ingrain and the latter two have immunities. Then, of course, there's Imposter with all the benefits and risks that it brings.
As for wall breakers, due to anti-setup being fairly commonish, you really want something that can hit hard with little to no set-up time. An example I used in Gen V was Choice Band Adaptability Entei who could outspeed and OHKO PH Gigas with V-Create or seriously maim Giratina with Dragon Rush.
