I've been using "kubuntu" ( which is the same as Ubuntu but with a different GUI ) for over a year now, Im happy with its stability and usability, also I had no security problems at all, the distro is well updated regularly and you will not have any of the headaches that windows malware causes !
Of course im not saying that its exactly heaven, but one can tolerate some minor problems from time to time..
I understand you need it for your daily use, what will you use it mainly for ? office apps or media playing or web browsing ? or all of them ?