hobbywing has come up hugely. they used to be a lot cheaper than the competition and that's how they got so popular, but they aren't cheaper any more and are considered just as good as any other top brand and are probably the most popular currently. personally i like to try different brands - most of my stuff is tekin but I also have maclan and castle mostly.
The only negative on hobbywing I've heard is that customer service isn't the best so if you have an issue it may not be easy to get service, however it's easy to hear bad things about customer service from just about any company if you look hard enough. I"ve personally had great cusotmer service from tekin recently.
Castle is aimed more towards the basher crowd - they offer only 4 pole motors, so if you're legit racing, you may be limited depending on the class. I think 10th truggy class uses 2 pole motors.
Castle's mamba X esc (not monster) is really good in my opinion, but if you can't use a castle motor then I wouldn't recommend mixing esc/motor brands - usually there is no problem in doing that but once in a while there can be - stick with the same motor and esc if you can.
You can also consider many other brands that make 10th scale stuff if that's what you're looking for.
they all perform comparably in my opinion. castle if you can run a 4 pole is probably the best value new by far - you can get a cheap sidewinder sensored esc with 1410 motor for like $120 new online - that's half of what you'd pay for another brand... You'll find that not many folks use castle for actual racing, likely due to offering no 2 pole motors, but for 4x4 sct and 1/8th classes I've seen a number of club members win with castle.
