Corporate FP&A + M&A Team or Boutique Experience?

Brief background: looking to break into IB, just graduated from a non-target in August with a B.Sc in Finance, no banking internships, kinda shitty GPA (3.1 cumulative, 3.7 major), no offers from FT recruitment.

So here's the dilemma: I currently have two offers in Charlotte, one with a mid-sized company (~5000 employees) working on their FP&A team as an analyst, but they're currently in the process of forming a separate M&A team with it being fully implemented within the next 6 months and I have been recruited specifically with the intention of moving me to the M&A team. My other offer is a 6 month fellowship with a boutique that specializes in M&A and consulting. Not sure of their deal flow which worries me a bit.

From a recruiting/hiring aspect, which offer would look provide better experience when applying for FT analyst positions at a MM or BB next year? I understand that my chances are still relatively low and that my best course of action to break into IB is the MBA route, but considering that, which direction would benefit me the most? Part of me thinks getting actual banking experience might be more useful, but without any idea of the deal flow, I don't feel comfortable relying solely on that idea. At the same time, the company looking to hire me for FP&A and M&A has made 9 acquisitions YTD, around 20 over the past three years, and has quadrupled their revenue in the same time frame. Albeit, the deals have been small (competitors only focused on one portion of the sector or individual divisions from competitors), but nonetheless, I at least know what to expect there. The other factor to consider is that the boutique position is only a fellowship/internship, so I'd be unemployed within 6 months, whereas the corporate roll is permanent with a slightly better salary. If an MBA truly is my best option long term, I would think the edge would have to go to the corporate roll, as the MBA would help me to transition from a corporate finance roll into banking, and MBAs always tend to be marketed as a ticket into a new career. Any advice or logical thought processes would be appreciated.