In SQL, is UPDATE always faster than DELETE+INSERT?

Question

Say I have a simple table that has the following fields:

1. ID: int, autoincremental (identity), primary key
2. Name: varchar(50), unique, has unique index<

Answer 1

What if you have a few million rows. Each row starts with one piece of data, perhaps a client name. As you collect data for clients, their entries must be updated. Now, let's assume that the collection of client data is distributed across numerous other machines from which it is later collected and put into the database. If each client has unique information, then you would not be able to perform a bulk update; i.e., there is no where-clause criteria for you to use to update multiple clients in one shot. On the other hand, you could perform bulk inserts. So, the question might be better posed as follows: Is it better to perform millions of single updates, or is it better to compile them into large bulk deletes and inserts. In other words, instead of "update [table] set field=data where clientid=123" a milltion times, you do 'delete from [table] where clientid in ([all clients to be updated]);insert into [table] values (data for client1), (data for client2), etc'

Is either choice better than the other, or are you screwed both ways?