This was years ago, so perhaps this info is outdated by now, but I'll share in case it's useful.
My ex-BIL was an HVAC guy. He said Nest products caused all kinds of headaches for HVAC guys. I don't recall what the nature of those headaches were, but I asked the same question of a number of his co-workers when they serviced our systems and they all agreed. They recommended Ecobee, and I do frequently see Ecobee reviewed very positively. I may be getting one myself soon.
I will say, however, that I'm a little skeptical of claims of huge energy savings. If you're already using a programmable thermostat - and you actually take the time/effort to program it - it seems like you're 90% of the way there. I'm sure there's some learning that a smart thermostat can do to eek out more efficiency, and for sure the ability to change settings from anywhere at any time is nice. But I'd be curious to hear whether people who switched really saved all that much.
FYI, if you're on MidAmerican,
you can buy at a substantial discount with the rebate priced in.