Right of First Offer or Right of First Refusal

It is not uncommon for Managed Service Providers or MSPs to be owned by multiple parties.  Normally, we see a technical person partner with a marketing and sales oriented individual.  They should have a buy - sell agreement.  Should it contain a "right of first refusal" or a "right of first offer?"  In today's MSP merger-mania environment, a right of first offer is probably the more fair method of resolving ownership succession.