Aftermarket. 10X the range and limitless expandability. Viper makes decent stuff, but look into Compustar as well.
Let me also add that, regardless if you decided to go aftermarket or factory, the installer is going to make all the difference. A tech from a dealer is generally "jack of all trades" on a car rather than an expert on any one particular part. A good aftermarket remote start installer has done hundreds and hundreds of installs of that exact model you're buying; possibly on your very same vehicle.
I had a RS in my old car and it was nice. It was from DEI, Do they still have to cut/splice into many wires or are they plug and play now with all the computers on the cars now? It's true with what you said, the install makes all the difference.
VERY few cars are plug and play. "T-harnesses" are made for select vehicles that prevents cutting into wires at the key cylinder, but most of those still require other connections to be hardwired. And the T-harness is especially pointless for the 14 Focus. A lot of the connections needed are at the BCM behind the glove box. This means, for example, the FLCAN or DBALL2 you'd use for this would have to be mounted under the driver's dash so the T-harness will reach the key cylinder.... and then you'd have to extend like ~8 wires way over to the BCM on the passenger side. Not the end of the world, but pointless when you could just forgo the T-harness and make all your connections on the passenger side.
But back on topic, a standard install of a full standalone remote start system will require some splicing, yes. Again, get a good installer and you have nothing to worry about.
You know what's kind of a nice setup.... the DBALL2+XL202+9211V remote kit. Pretty darn easy to install. No heavy gauge wires. All can be done at the BCM. And that remote kit is just a small one-button keyfob (since you already have to carry the lock keyfob on your key). But the kicker is that keyfob is RF. So you'll get 2000ft range and 2-way confirmation if the vehicle actually started. Adding up the dollar amounts, it's probably not going to be too much cheaper than a full remote start brain setup, but it'll be a cleaner install for sure.