It depends on the value proposition I want to bring forward. If I am going with the whole "we'll save you money" pitch, I'll start with a CFO or Director of Finance. If it's regarding document management or a fleet replacement, I'll start with IT Director/IT Manager and go from there. Larry Levine's teachings on LinkedIn have been really useful with cracking into appointments/conversations with these types of people. C-level execs and directors are very career-orientated, so they tend to have juicy LinkedIn profiles with lots of information to start that relationship building process!
Some SMB accounts are too small for IT or Accounting, in which case I speak directly with the owner.
For inbound leads, I'll work with whoever requested the quote and work directly with him or her. If someone is asking for a quote, it means they've been put in charge of collecting the information and a decision maker trusts that person's ability to make a recommendation, even if they are not directly signing off on it.