Before deciding what is best, look in the database here to see if a scanner with that budget is even *capable* of receiving those systems in your area.
If they are encrypted, no scanner will work.
If they are trunked, you'll need a scanner that will do trunking. Otherwise, a conventional lower-cost scanner will do.
If they are running P25, that will also guide your decision as they are usually quite a bit more expensive than your $150 budget, unless you can get one used.
If the systems for your area show that they are not encrypted, and not using P25, if you were willing to spend $20 more, either the Radio Shack Pro-163 desktop/mobile or Pro-164 handheld would fill the bill of monitoring conventional and trunking systems. This is just an example, there are many others.
It also depends on just what type of Police activity you want to monitor - local municipalities might be running a very simple conventional system, whereas county-wide systems could be using trunking / P25 etc - it all depends.
With a $150 budget, it is very important to determine just what is used in your area so you don't waste money on a scanner that can't even pick up what you want, or perhaps spend too much on features you don't need.