My car has 28km on the original Continental Sport Contact 2 tyres. I estimate 2-3 km more from the fronts but the rears still have around 40% tread remaining. I have no complaints with the Conti's but I don't think they are worth the cost here in Au.
I have had Hankook tyres on other vehicles in the past and was reasonably satisfied with them. These new 107's look the goods and the blurb reads OK. Silica compounded etc. Price is good. It comes down to how others find them in use.
I will replace front and rear together. Just something I always do.
There are a number of other options available for the fronts 225/40/18 but rears 255/35/19 are more difficult. e.g. Cannot source Goodyear or Dunlop.