Slow burn and instant attraction offer two different ways into a romance. Neither is automatically better. They simply create different reading experiences.
In a slow burn, the relationship develops gradually. Attraction may be present early, but trust, honesty and commitment take time. Readers enjoy watching small moments accumulate until the relationship reaches a turning point.
Instant attraction creates an immediate spark. The characters may feel drawn to each other from their first meeting, but that does not mean the relationship is already secure. The story can explore whether chemistry becomes compatibility and whether attraction survives the discovery of each other's flaws.
A slow burn often gives more space to anticipation and gradual character change. Instant attraction can create momentum and make the emotional question less about whether the characters want each other and more about whether they can make the relationship work.
The best choice depends on your mood. If you want tension that builds over time, choose slow burn. If you enjoy an immediate connection followed by complications, try instant attraction. And if you like both, there is no reason to choose only one.