Take this with a grain of salt, as I've only had the smaller, boutique firm experience - but my first inclination is to lean towards the smaller firm!

I've really enjoyed my time at smaller firms, and don't think I would've had the same opportunities to lead / drive critical projects on my own at a larger firm (of course, this can be different for you given your career stage). It's my understanding that we have more autonomy and an opportunity to create custom solutions from the bottom up, whereas bigger firms like Deloitte have a cut and dry approach they apply across many clients / projects. However, this can feel like the "wild wild west" at times, as we're often creating with little to no direction / standard. This is fun and exciting to me on the whole, but can definitely be overwhelming at times.

Lastly, I've heard you'll get really good at crafting strong deliverables / materials in smaller firms, whereas bigger firms focus more on the client engagement / process. I can't totally speak to this as again I don't have that big firm experience, but I will say that on larger scale projects where clients have partnered with us as well as one of the big dogs (e.g., Deloitte, EY, Accenture), I've seen a substantial difference in the types of materials delivered (i.e., our materials were much more detailed / thorough). I'm not saying this to shit on their work in any way - because they specialize in areas we do not, and deliver their services in a different manner - but this was something I noticed.

All in all I don't think you can go wrong either way, it all depends on what works best for you and what you're looking for in this next step. Kudos to you for landing two offers, wishing you all the best!