A bird in the hand
Within the current market, I am sorely tempted to suggest that you plump for the company that has offered you a role. The big players will always be there in the future and what you want here and now is the opportunity to move into the customer relationship management (CRM) market.
The only proviso would be the state of the company that is making the offer. You mention that it is a medium-sized firm with its own product. Is it a recognisable name and has it got a solid financial standing? Many people have been put in the invidious position of moving out of a secure role only to find themselves casualties of today's uncertain economic climate.
Conversely, without previous CRM experience, is this the only company in the market that is willing to take you on and train you? Have you had any positive feedback from "players" that suggests they would be interested in you?
I would take a role with a medium-sized firm that is willing to invest in me, while knowing that the only thing I would be out of touch with is the latest release of the leaders' products.
Employers are looking for business knowledge of the market - specific packages at this level are less relevant. Consultancy skills are always highly sought-after, and with that knowledge comes the opportunity to move into more senior roles such as project management.