Intrusion Detection is one of the most common approaches used in detecting malicious activities in any network by analyzing its traffic. Machine Learning (ML) algorithms help to study the high dimensional network traffic and identify abnormal flow in traffic with high accuracy. It is crucial to integrate machine learning algorithms with dimensionality reduction to decrease the underlying complexity of processing of huge datasets and detect intrusions within real-time. This paper evaluates 10 most popular ML algorithms on NSL-KDD dataset. Thereafter, the ranking of these algorithms is done to identify best performing ML algorithm on the basis of their performance on several parameters such as specificity, sensitivity, accuracy etc. After analyzing the top 4 algorithms, it becomes evident that they consume a lot of time while model building. Therefore, feature selection is applied to detect intrusions in as little time as possible without compromising accuracy. Experimental results clearly demonstrate that which algorithm works best with/without feature selection/reduction technique in terms of achieving high accuracy while minimizing the time taken in building the model.