What kind of people makes you happy?
The key in this question is "you", so this makes a very interesting yet personal question...
Having interacted and observed a fair share of people (I am a bit of a self-proclaimed mind-reader :), I'd zero-in on following characteristics of nice, tolerable people whose company makes me happy (actually would make anyone happy!) -
(1) They are REAL! Which means they are not fakes, hypocrites, back-biters or plain show-offs. REAL people are very hard to find and a big thanks to our virtual-worlds for it.
(2) Enthusiastic, smiling, bubbly. or other such adjectives to describe a "positive energy". When there are four of you sitting, you need that rub-of-energy from someone to really feel good about that time.
(3) Compassionate. This is one word which describes a LOT and means different to different people. Here I use it to describe people who are genuinely concerned for you, or anything else that they care for.
Hard to find all 3 qualities in the same people and at the same time. But if you come across such rare people; then don't miss out on them!