Bruce Lee was disciplined in Kung Fu..but if it were not for his acrobatics and flashyness, would not have made it into the mainstream.
Originally he DID think KungFu was the best, but later he ackowledged that as a biasness and made his own martial art- Jeet Kun Do, his synthesis of the most 'realistic' tactics from all styles. (including taekwondo, judo, aikido, etc)
Not to take anything away from bruce, he's one of my heros and one of the best fighters of his time i'm sure, but people underestimate the advantages of size (see weight divisions...) and i'm sure a good 300 lb trained fighter would beat his 140 lbs more than not.
(Although it doens't matter how big u r...a luck, clean strike to the chin will KO anyone- so anything is possible..just not likely)
but anyway...
The martial art is only as good as the one taking it. Anyone can raise the bar for their discipline. The problem is not limiting urself to a martial art's "style".
I'm a blackbelt in TaeKwon Do, but in a real fight, i know better than to just kick. I box and wrestle with friends and give those much more priority in my fighting mentality when i spar.
another important point is using what u can be good at.
someone 5'5 isn't going to get much use from TaeKwonDo. Someone tall and skinny isn't going to a prodigy in judo. Someone 300 lbs is going to have a a hell of a time learning jeetkundo, and someone completely muscle bound is going to be much less maneuverable in grappling situations.
But as far as the UFC goes, Brazilian JuJitsu and MuayTai kicking boxing (spelling on those) are the most favored to know.
But the UFC is not w/out its rules. No pinching, biting, groin-hitting, strikes to the back of the head, gouging, and fishhooks to mouth, etc.
Martial arts heavy in pressure point skills such as HapkiDo and Aikido are severly handicapped in the ring, but its for reasons not unjustly designed. It is demeaning for "entertainment" and "sportsmanship" purposes if someone can escape a rear naked choke by twisting the groin or sucking someone's eyeball out their skull (which is very, very possible and actually a tecnique of DunMak Kung Fu [again bad spelling])
-------------
the best answer i can give you is KickBoxing(for ur upright) and JuJitsu(for ur ground) everything else, u only need the basics of for occasional use: such as judo or sumo/wrestling.