I have, or have been through, at least a half-dozen scan tools not to mention that I worked for an auto manufacturer and had access to all their (then) current tools. At least part of what you need to think about is what brand(s) of cars you need to use it on. I have a small generic scan tool that I keep in the car. It's saved me twice while traveling, enabling me to diagnose how serious the problem was and/or delete the code to get me to the next exit or even all the way home. I also have a Snap-On MT2500 (purchased used, in pieces) that served me well for OBD 1 & 2 up until can-bus (2006ish). Since then I have operated with ForScan for my Fords and Vag-Com for the VW's (both are brand specific, almost, dealer level tools). We recently added a Hyundai, a Chevy, and a Subaru to the fleet so I went looking for a tool that was pretty capable for those brands and wouldn't "break the bank." Cost is a relative term and I quickly realized I'd need to spend at least $400 to get where I wanted to be, i.e. bi-directional controls and able to access proprietary systems.
I ended up with an Innova 5160RS. There are similar variants of this model number depending on the seller. It has bi-directional controls and accesses most of the proprietary systems on the cars we own. I have also found, for simple operations, it's often faster and easier to use than either of the proprietary systems. For example, It gets chosen frequently for resetting VW service indicators. It has an easy-to-read screen, simple operation, and links to Innova's repair database. I haven't really used that feature yet so I can't comment. If I still had my auto repair shop, I would probably have a tool like this for daily use.
The $weet spot for really capable scan tools seems to be in the $400 - $800 price range. If you don't need that much capability, you can get into a good tool that will probably serve most your needs for $100 - $300. I hate to make this sound so complicated but you really need to research a tool that performs the functions you need and works well with your car brand(s). If you look for it, most of the reputable brands have a coverage chart that will give you a good idea of what it will do on what brand/model of car.
Lou Manglass