For new development staff, I advise going BIG. That is, starting out with an BIG organization, large enough to support your growth and development as a fundraising professional. At the early stages of your career, it’s critical to have access to training and education opportunities to round out your technical knowledge -- such as, applying statistical analysis to your donor file --as well as to acquire expertise in areas like accounting and regulations governing charitable solicitation. Like any field, fundraising has its own specialized areas; planned giving and grant-seeking are just two. Gaining knowledge in these and other areas will make you an essential player in any development office.
And that's where a big organization come in. As you commit to expanding your knowledge base, it will be much easier if your organization supports your efforts -- and not just in theory. A large organization ($10 million plus), in most cases, is in a better position to underwrite your training and to give you work time to complete it.
As someone who benefited early on from week-long courses in planned giving, marketing, and major gift development (thanks United Way of America!), I can attest to the benefits of early-career training. It helped immensely as I moved to other organizations and moved up the ladder.
Of course, if you opt for a small organization, you can still access lots of free and low-cost training (check out the Foundation Center), but the reality is that in small shops, the profit margin is slim, the staff is stretched, and time off for career development may be difficult to manage. In a bigger organization, you may feel lost in the bureaucracy and you may sacrifice some autonomy, but the payoff in learning will be worth it. And you will be a lot more valuable to the next place you work.