e72bfd15_Cassandra_vs_HBase___WhyNosql__Cassandra
[HBase] If your key's first component is time or a sequential number, then hotspotting occurs. All of the new keys will be inserted to one region until it fills up (hence by causing a hotspotting problem). [Cassandra] 
Even if you use TimeUUID, as Cassandra load balances client requests, hot spotting problem won't occur. (All the client requests going to one server in a cluster is known as a hot spot problem).
Cassandra vs HBase | WhyNosql
Cassandra