Speed Force makes this a non-contest — Flash is too fast for even spider-sense to matter.
Spider-sense is incredible precognition, but it can't help when the attacker is moving at lightspeed. Flash can think, react, and strike millions of times before Peter's spider-sense can translate the warning into physical action.
This is the ultimate 'precognition vs. overwhelming speed' matchup, and speed wins. Peter's spider-sense fires, but his body physically can't move fast enough to dodge a Flash-speed attack.
Speed Force makes Flash untouchable and gives him devastating offense through the Infinite Mass Punch. Phasing bypasses web-based defenses entirely.
Spider-sense provides advance warning, but Peter's body can't react at Speed Force velocity. Peter's intelligence is world-class but irrelevant against someone who moves faster than thought.
Flash wins instantly. Spider-sense knows the punch is coming but can't do anything about it at lightspeed.
The Flash also fights
Spider-Man also fights