tl;dr HotDQ is a good adventure, especially for new players.
First, a little background to frame my opinions. My group of long experienced players is halfway through HotDQ and planning to complete the whole Tyranny of Dragons story. I've read through PoA and half of OotA. I think they are all good modules while being very different from each other.
I started out by making sure the players were happy with the idea of being the champions who might have to sacrifice themselves for the good of the world. Going in with that agreement makes the railroady aspects less of a bother.
So far HotDQ has been fun but very dangerous. The opening chapter could easily wipe out a 1st level party several times over. To help with that I had clerics in the temple provide several Cure Wounds and the town mayor gave the party access to his armory so they were able to select armor and weapons not normally affordable to 1st level PC's. Other than that, we've been enjoying the module and only had one PC die (the number of death saves has been far higher).
Tyranny of Dragons will require a fair amount of prep work. The books are not written linearly so you will need to study them and make notes. In some places, the books spread key bits of information throughout a chapter so you have to read and understand the whole section before the game gets to that point.
For a group with brand new players, HotDQ is a very good adventure. There's plenty of room for the DM to add extra stuff so it doesn't feel so linear and the story doesn't leave the players puzzling over what to do next. The PoA sandbox could easily turn bad for the characters since the encounters escalate in danger so going "backward" could put the PC's into more than they can handle without any warning. It is up to the DM to adjust as needed so the players have a chance. For instance, I'm pretty certain my players would find the slightly hidden node entrance in the first temple and head straight for something intended for higher levels.
Generally, I like sandbox games for homebrew campaigns (I have many adventure plans that have never been followed by the players), but modules, especially big adventure path style modules, need players to be on board with the story. Coming from that perspective, even PoA is railroady in that you need to deal with all the module's parts in an order that is possible for current levels, or fail.