First of all, both Spark and Redshift are different from each other catering to different users, and different needs. Apache Spark is Big Data processing framework, which is used to stream and process real-time data parallelly, reading into memory thus enhancing the performance nearly 100x that of Hadoop. Whereas, Amazon Redshift is an analytical database, which is offered by Amazon as a “fully-managed” service to store a huge amount of data, from where you could use it for processing. Both are used in the Big Data domain but serve different purposes. So, there cannot be a verdict saying one is better than the other. If you wish to know more about Apache Spark, check out the Apache Spark tutorial, and if you wish to get certified in it, then check out the Spark certification course from Intellipaat.
Also, take a look at a video on Spark training to get a better understanding.