Alright first question is does your local utility company offer a rebate program for installing a smart thermostat? If they do and you plan on taking advantage of the program you might want to take a quick look at their approved thermostat list before you buy. Around here my utility company offers a $100 rebate per thermostat for up to two thermostats per household. I have two thermostats so I was able to save $200 last fall when I upgraded ours.
Essentially paying $40 for the upstairs Honeywell unit and $80 for the main floor Nest unit. A significant savings.
Now that that is out of the way it is hard to tell from your picture but it appears there are four wires currently connected to your thermostat. Do you know if there are more wires available behind the face plate that are not in use? It has been my experience that when installing a new smart thermostat you really need a fifth wire in order for them to work properly.
If you are looking a simple thermostat with basic smart functionality the
Honeywell Home RTH9585WF1004 is a good option. It also has the ability to run your humidifier but ONLY from the app NOT from the unit itself. I've been using this unit since last fall for the upstairs HVAC system and it has worked really well but just remember you NEED a fifth wire in order for it to work properly.