Which tool is best to use for authoring? The answer 'it depends' is very applicable here. One key difference that might help you decide - when authoring is done in the Operations Console all changes that are made get applied as they are made - which can cause the RMS to be extremely busy. If you are only making a couple of changes, no big deal. If you are making bulk changes - this quickly becomes a big deal and can impact performance while the RMS keeps up with the authoring work being done.
For bulk rule creation there are a couple of options to avoid the performance hit on the RMS
-Author all rules from a console in a development environment. When done, export the modified management pack and import into production. -Use the authoring console. One key advantage to this - when management pack objects (MPOs) -rules/monitors/etc - are created in the Operations Console the name of the MPOs as saved in the management pack do not have a user friendly name - they all start with UI Generated..... If the management pack is opened with the authoring console it will be difficult to know which MPOs you are looking at. This won't be the case when authoring MPOs directly in the authoring console.
My preference - use the authoring console for all MPO authoring - this is what it was designed for and if you are planning to do any somewhat serious management pack work it is a crucial tool to learn. The operations console is fine for overrides and such but is not ideal for authoring.