I've just benchmarked Spark and Impala. Same data (in s3), same query, same cluster.
Impala has a long load time, since it cannot load directly from s3. I have to create a Hive table on s3, then insert from that to an Impala table. This takes a long time; Spark took about 600s for the query, Impala 250s, but Impala required 6k seconds to load data from s3. If you're going to go the long-initial-load-then-quick-queries route, go for Redshift. On equivalent hardware, that took about 4k seconds to load, but then queries are like 5s each.
