I had Conti GP4Seasons when I bought my new bike, the guy said they were the best all-weather training/race tyre.
As far as I'm concerned, they have the worst wet-weather grip of any tyre I've ever used, they scared me several times and then finally I came off at Tour of Wessex, so they're off the bike but kept in the back of the garage as just-in-case spares.
They also p*nct*red pretty regularly (I even got one on the turbo, presumably a thorn already on the tyre...) and were nigh-on impossible to get on or off Fulcrum or Shimano rims.
But on other websites, other people have said how absolutely brilliant they are and they swear by GP4Seasons and GP4000s !
So it would seem to be very subjective and personal - the same tyres for different people give different results - your weight, pressure you inflate to, bike/riding style, etc. Maybe even the roads you ride - are you in a wet or dry part of the country, do the council maintain them, does green slime grow on them ?
For myself, I use
- Pro Race 2 on my best/sportive bike and they seem pretty good. The red ones are over-the-top bling !
- Vittoria Open Corsa CX Team TT on TT/tri bike and they're excellent, fast and reassuringly grippy even in wet, although seem to have a reputation for being a bit fragile/high wear, which is OK on a race bike
- Vittoria Rubino & Zaffiro Pros on 2nd/winter/commuting bike and they're brilliant, have done enormous mileage and are really worn with lots of cuts etc but hardly ever p*ncrt*re, tons of grip, really predictable. Also a lot cheaper !