'-T2' would be the most appropriate option for stealthy scanning in an IDS-rich environment. It is slower than the default '-T3', thus sending packets at a lower rate which reduces the chance of triggering alarms. '-T0' and '-T1' are even slower and might be less likely to raise alerts, but they can significantly increase scan times and may cause timeouts. '-T4' and '-T5' are far more aggressive and would likely increase the risk of detection.