As outsourcing becomes more prevalent in the pharmaceutical industry, this question becomes more and more important.
There will no doubt be differing opinion on this. Many experts will swear blind that companies of a similar size work best together and to some extent I think they are correct. The rationale behind this, is that, if companies are of a similar size, they are more likely to have a similar culture and therefore will work better together. Another point often raised, is that if you work for a smaller business, they may be more highly valued at a smaller service provider, than at a larger service provider where your business needs may be lost amongst those from a larger number of customers, some of which will most probably include big pharmaceutical organisations. However, having said this, I have seen some excellent relationships between large CMOs/CROs and much smaller customers, so this model can work too.
A key way to determine whether a CMO/CRO of any size is right for your needs, is to get verbal references. In fact I would suggest that you do this in anycase. Especially if this is for a large, costly piece of work like clinical batch manufacturing. The key thing here is to ask your shortlisted prospective service providers, for 2 or 3 references from companies of a similar field and size to yours.
Also don’t forget also that all CROs and CMOs require significant management with frequent communication playing a key role. Along with a good technical fit, a good working relationship will help your project through any challenges that may arise.