A. Bloomberg is the one used by pros, but if you can't afford the $20.000 per year fee, try YCharts, a new web-based service that is aiming to be the cheaper version of "Bloomberg".
YCharts is especially useful for someone to research data to craft portfolios. It costs $50/month for the "Gold" version and $200/month for "Platinum" version. The tool is entirely online, and although it's not quite perfectly real time in some of its data - YCharts is about 10 to 15 minutes behind Bloomberg, but if your goal is on wealth management than real-time stock trading, that may not be an issue.
For most ordinary investors, I recommend you using Morningstar to research mutual fund research and YCharts for equity research.