Only you can be the one to decide which company is best for you. You need to interview many different ones in order to make this decision. You want to go with a company that offers the most training and support and will help walk you through your first few deals. You also want to make sure that the company you choose is giving you a decent split without all sorts of desk and transaction fees. Find a company that has a reputable name and following as well. Keller Williams happens to be one of the better ones out there and Im not sure if all of their firms or just some of them, offer profit sharing as well.
Regardless of which one you choose it will be difficult to get that first deal. Just be patient and make sure to constantly remind everyone you know what it is you do. Get a lot of business cards and everywhere you go, fairs, supermarkets, restaurants, etc., walk up to everyone and hand them a card, introduce yourself and what it is you do. Pick an area you know well and go door knocking passing out pamphlets and cards.
Keep at it be patient and dont give up. Its gonna suck for a little while but once you get that 1st one it will just get easier from there. Best of luck to you.