My thoughts are directed toward the issues of working with Structural, Civil, and Mechanical-Electrical [M/E] consultants. Other specialties like food service, acoustics, lighting, graphics, landscape have a much more limited scope and finding a firm with a good reputation or who has worked with firms you respect is usually good enough. BTW that concept might be considered a starting point in your search for any consultant. ’Who works for the firms you admire?’
The nature of the beast for M/E firms is that they need 3 times the number of projects as you do to be the same size as you. M/Es that do process engineering, water treatment etc will need a specialized building design department or they may never ’get’ what the project requires. You want someone who does lots of this kind of work so you don't discover they have a blind spot right where you need expertise. Structural and civil firms may have other types of clients so the issue isn't the same.
Structural consultants have rarely been an issue. Maybe we have been lucky. The exception is if they are much larger than you. Then there is a tendency to speed ahead of you, which makes for a lot of changes for someone. They will resist being the ones who change because ’we did what you asked us to do’. The problem is that they aren't used to stop-and-start and client whims, because their work is inherently much more straightforward.
Civil is similar to structural with the difference that a structural engineer is used to working with some small scale fussy stuff. Small scale to a civil engineer is anything less than a football field in size. You might think about how a curb should terminate; they never will. If this stuff is important to you, you may have to give them the notes or details you want to see on their drawings. Just saying, that’s the tendency.
I think the right ratios are 3:1 for the M/E size to your size; and 1:1 for the Civil or Structural size to your size. These are just guidelines and many other things are more important than size. The next post will touch on those issues.