Long-term goal is AM. Should I start in ER or AM?

I have a full-time ER offer at a lower tier BB. If I take this offer, I plan to stay in ER for about 2 years, and then exit to the buyside, preferably at an AM firm. Long-term, I can definitely see myself as a portfolio manager.

However, I've also been getting plenty of interviews for development/rotational programs at buyside firms, such as AM arms of top insurance companies, as well as decent AM firms (ranging from $50b - $500b in AUM). 

Given my long-term goals and desire to exit to AM, am I better of starting off in AM? Or should I get that 2 years of sell-side experience? Are there any advantages of starting off in ER (other than slightly higher pay)?