I can’t begin to tell you how many terrible things you can avoid by starting your apps out using an optimistic isolation level. Read queries and write queries can magically exist together, at the expense of some tempdb.
Yes, that means you can’t leave transactions open for a very long time, but hey, you shouldn’t do that anyway.
Yes, that means you’ll suffer a bit more if you perform large modifications, but you should be batching them anyway.
Optimistic concurrency is huge—definitely worth the top slot in Erik’s list.