We were in the same boat 3 years ago, very hot market, asked 3 realtors to present their case. We went with the prepared, professional go-getter (A in your case). Never regretted it. In our case, B was a nice person, but she wasn't prepared, and in real estate you have to be ready and act quickly. I was afraid that B would be too laid-back and we'd miss out somehow. While it's great to feel comfortable with someone, you have to be confident she'll get the job done. As for the work she helped you with - nice, but that isn't something I would expect from a realtor. Her job is to sell your house.
As an aside, we had the third option, I'll call it C, and we liked them, too. I just had a gut feeling about A and I felt she did a great job. One of the reasons I liked her was she stayed on top of everything, including my DH (who was working on getting the house ready for the market and tends to be kind of slow and deliberate). It was just what we needed to get going and get the house on the market. It sold quickly and for a price above asking.
Regarding investors - you don't have to go with an offer from an investor if you don't want to. Our agent had some investors and we turned them down because the offer was for the asking price and we knew if we waited we'd get a better price.