Hi Christopher
There are pros and cons to both options.
Really, it's down to factors such as how the actual words read, brand or non-brand preferences, how it's going to be marketed, any surveys carried out...
When talking about your business/website and marketing offline, how would the web address be conveyed; "one dash two dot com" or "one two dot com".
Having a hyphen/dash in the domain name can cause confusion and memory issues for some, usually without it reads just fine in search results.
Some examples:
Well known brands indeed, however the concept of not having to rely on a hyphen/dash can be seen here, it can and does work for some, though granted not for all.
So another option if your preferred choice is taken ( e.g. onetwo.com ) is to choose something else, such as onefive.com if you'd like an option rather than a hyphen/dash.
Obviously this depends on Branding, could be that you really need the words "one two" in there.
Bear in mind that exact match domains don't matter so much for SEO as they once did.
So a tough call, go with what you believe to be best for the combination of both User Experience and your Brand.
Hope that helps,
Regards
Simon
