So this is by no means a complete list, but ever since I setup my HE and integrated water sensors, I've been testing notification options. I want to know immediately when there's a leak around a hot-water heater, sump, icemaker, washer, A/C etc...
As far as requirements, I just wanted to know within seconds if I had a leak someplace. I don't have Echo \ Alexa integration setup quite yet, but I also want notification when I'm away from the house.
Hubitat Phone App Notification :
I started with just the standard Hubitat notification to the app on my phone, however my phone is unreliable some days when it comes to installed apps. I probably just need a new phone, but I'm always a bit annoyed at the need to upgrade $500+ devices on a whim just because they've gotten "slow".
Anyway, I digress...
So, Hubitat App - not thrilled, it requires an App, and for my phone (and my wife's) the notification is a bit laggy. Some days it fired within seconds, some days a minute or more. Again, I blame my phone...
Pushover :
I didnt realize at first that Pushover was another app, I thought it was an API for use with SMS push notifications like Twilio, so this falls into the same category as the Hubitat Phone App Notification. Nice for some, but not for me. The only thing I did like about it was the ability to create "ringtones", add them to my account, and pick a different notification sound when triggering a notification to my phone. Cosmetic, yes, but the Homer Simpson DOH! sound is pretty unmistakable with all the other electronic notifications going on in the house these days.
Twilio :
I've always been a fan of Twilio, so I'm a bit biased, and even though there's a cost, the spend for a single SMS message is inconsequential. If I was doing marketing, maybe a bit more costly, but as far as notifications go I love that I can simply send a text message. Of course this relies on text messages being delivered in a timely manner, but we've never had a problem with this, even living in the country, so unless there's some wide-spread cellular outage that might make my water leak less important, I've been leaning toward Twilio as the solution for alerting for me. Add to this the fact the updated driver supports phone calling, I now have a way to add the Twilio phone number I pay for to my circle that's not ignored when my phone is on DND, and I can get a call AND a text when things go pear shaped.
SendGrid :
I figured I'd try SendGrid as well, since my normal day-to-day involves monitoring eMail all day long, and since it's affiliated with Twilio I expected a quality product. I was not disappointed. Another pay-for service, but it's been amazingly reliable and fast. Yes, I know, email speed is dependent on a number of things, internet connectivity, number of hops, spam filters etc... but so far, no complaints with delivery. The only caveat I've found is that I can pretty much email anyone I want from the app, however trying to send an email to the address I use as the FROM address basically results in the message going AWOL.
The winner ?
Twilio.
Your mileage may vary, but for me, not relying on a phone app and using SMS means that I could change phones, as long as my number remains the same, or pretty much switch to a pager (that supported SMS) if it came to that, and still get reliable notifications.
Again, this is just my shoot-out between the apps \ options I have today, it might change in the future, but for now, I am sticking with my current configuration. Which, by the way, is a SMS message with Twilio, push notifications to both the Hubitat and Pushover Apps, along with a phone call. I'll probably add Alexa too 
What's next :
Well, seeing how I spend all day at my PC, I'm thinking I might play a bit with Toast notifications on Win 10. My phone is on DND all day while I talk to customers, but a toast notification popup on my PC while I'm working to tell me that my house is flooding would be a nice addition to monitoring.
