Best counter-picks
These heroes are listed as strong answers into Sombra.
Tank
D.VaD.Va's Fusion Cannons has a very wide spread, making it easy to reveal Sombra while she's stealthed
D.MonD.Mon can deploy Barrier to cancel Hack, reducing Sombra's ability to stop her engagement.
Damage
CassidyCassidy's Flashbang can punish Sombra when she decloaks
SymmetraSymmetra can prepare for Sombra's flanks by placing Turret turrets
MeiCryo-Freeze can survive Sombra's burst. Translocator cleanses Mei's freeze
ShionSupport
MoiraMoira's primary fire can easily reveal stealthed Sombra. Sombra's hack can be cancelled by Fade. Sombra has difficulty winning 1v1s against Moira
KirikoKiriko can cleanse Sombra's hack with Swift Step or Protection Suzu
BrigitteBrigitte can interrupt Sombra's hack by facing her shield toward Sombra when she attempts to hack
Favorable targets
Sombra is listed as performing well into these heroes.
Tank
SigmaSombra's hack removes Sigma's abilities, making him vulnerable
Wrecking BallSombra's hack is extremely effective against Wrecking Ball, disabling his mobility and shields
DoomfistSombra's hack disables Doomfist's abilities, making him very vulnerable
Damage
AsheSombra can easily flank Ashe and force close-range fights. Translocator cleanses Ashe's burn
PharahSombra's hack grounds Pharah, putting her in danger
WidowmakerSombra can easily flank and pressure Widowmaker in close range
Support
LúcioSombra can temporarily disable Lucio's wall riding by hacking him
Jetpack CatSombra's primary fire is hitscan, making it easy to hit airborne targets
AnaAna has difficulty dealing with Sombra's flanks. Even if Ana lands Biotic Grenade, Sombra can cleanse the anti-heal with Translocator