Update performance: clustered versus covering index
Under the covers clustered and nonclustered indexes are the same. The clustered index just has the additional property that is is guaranteed to INCLUDE all columns. Therefore the data does not need to be maintained somewhere else. So, a clustered index and a nonclustered index that INCLUDEs all columns are virtually the same from an update cost perspective. 

However, every index needs to be maintained if it contains a column that was changed during an updated. That means, the more indexes you have, the more expensive updates get. 

So in your situation, I would try to keep the number of indexes to a minimum. That will help update performance more than worrying about if a particular index is better clustered or covering. 

That all being said, your updates still need to find the row(s) to update as quickly as possible. Because you have two orders of magnitude more updates then select, updates should be looked at first when designing the indexing strategy. After they are taken care of, look at providing the minimal number of appropriate indexes for the read queries.