Different ones work for different people, because the features do vary quite a bit.
Here are some of the areas where there’s the most variation:
One) cameras or only sensors? In the low-cost group, even some that have optional professional monitoring, only some offer sensors. And some of them have just still picture cameras, not video.
2) Monitoring contract, no monitoring, or optional. A lot of people like the ones where you can turn professional monitoring on for short time, such as if you’re away on vacation, and only pay for that period.
3) if professionally monitored, can the service also call the fire department or only police? This is a big deal for me, because my primary concern is professionally monitored fire safety as I am quadriparetic.
Many cities have limited the ability of third-party services to call out fire equipment because they get too many false alarms. So the third-party service is only allowed to call a police officer for a drive-by, which adds significant response time.
The big name contract companies like ADT can call the fire department directly in most jurisdictions, but that’s not true for most of the low-cost DIY systems. For example, at the time of this writing, scout, which is the one which has an official integration with SmartThings, can only call police, not fire.
4) does the system send its notifications via cellular or over the Internet? If it’s over the Internet, the system probably won’t work if the power is out or even just if the Internet is down. Many low-cost systems are free if notifications are sent by Internet but have a small monthly charge, like 9.99, if you want cellular service, even to your own phone.
5) does the system have integrated smoke alarms? Many of the low-cost DIY systems do not.
Six) can you use your own cameras, or do you have to use specific models? Again, there’s a lot of variation on this. Plus all the issues about securing video feeds from hackers – – lots of variation on how the different location services handle this.
7) exactly how does the system get armed and disarmed, and is there an adjustable entry delay? Some low-cost DIY systems can only be armed/disarmed it from the phone app. Many also have a button fob. Some have a keypad.
This is one of those features that matters a lot to some people and not others. It really depends on household composition, whether you’re likely to have someone like a dog walker coming in and out, whether you have small children, whether one household member has physical challenges that means they need more time for the entry delay, all that. But again, this is an area where there’s a lot of variation among the different low-cost systems.
Eight) is there an IFTTT service/channel?
9) does it work with echo? Some do, some don’t, some people don’t care, some people care a lot.
10) does it integrate with home automation, and if so, to what degree? Again, lots of variation on this. In my own case, I’m happy with a completely separate security system as long as that security system is itself stable and reliable and has the features that I want. But other people want everything integrated.
So again, you just have to find the one that is the best match for your own needs and preferences.
Sorry I can’t be more specific. Many people have a favorite security system, but it might not be one that would work for someone else, such as in my example of requiring a professionally monitoring system that can call the fire department directly. 
