I've done Thai as part of my MMA training and I've done Kickboxing, but I've never done or rated any type of Karate. I've seen Kyokushin, and don't see any similarities other than you kick and punch your opponent.
I don't rate Karate at all. I think that any martial art where you stand in front of your instructor throwing single punches and shouting is pants.. Don't get me wrong, its awesome for the individual who wants to get fit and be active, or for a child, but as a fighting sport there are better choices. This is just my opinion.
We have two karate black belts in my work, they're both fat (not that that's a problem, but for someone trying to convince me that Karate is good and they're the guys representing it I just think that they're full of shit) and seem very narrow minded when it comes to fighting sports. One of them argued that some grand master karate guy could beat a top UFC heavyweight in a no holds barred fight... he seemed completely deluded to me.
Unless there's something I don't know, but having a 'martial arts' background with Kickboxing for almost 10 years and MMA for 5 I just don't see how Karate is even comparable to an actual full contact real fighting sport like Muay Thai.
I'll agree with most of this. I think the main problem with Karate is the way it is trained, not necessarily with the techniques. If more time was spent impact training on pads, hard sparring rather than point sparring, and on conditioning / toughness, you'd have a lot less fat black belts, or 7 year old black belts, which I think is a joke. From what I understand, that is more like how they train in Kyokushin, which has produced some quality fighters over the years, including one of my favourites Andy Hug.
My son wants to do Karate, because it is what the other kids at school do, and I won't let him, because because I know most of the clubs will be shit (and this is coming from a blackbelt!). So he does Judo, where they have sparred / randori from day 1, getting used to contact, rough and tumble and resisting opponents. Of course, Judo is not a complete art, but couple it with boxing or Thai boxing and you won't have too many problems, from a self defence perspective. Competing in MMA obviously requires far more in the way of skillsets, but for keeping yourself safe on the streets or in a school playground scuffle, Judo + boxing / thai should be sufficient, in my opinion.
Back to the original point though, Kyokushin, or one of it's offshoots would be one of the better choices in Karate, providing you can find a decent club, it's full contact, hard conditioning, techniques are battle tested in full contact competition, and if one was to switch from Kyokushin to Thai, I'd reckon they would have an easier time of the transition than say, someone from a Shotokan, Wado or McDojo background.