First of all the jury is still out on whether even Christians go to Heaven. The Bible is rather ambiguous on the subject. The same goes for Hell. Most of the imagery we have for these places has developed over the years since the Bible was written. Christianity offers salvation it is true, but speculation on the exact nature of that salvation is just that – speculation.
The fact that a believer is happier than a skeptic is no more to the point than the fact that a drunken man is happier than a sober one. The happiness of credulity is a cheap and dangerous quality of happiness, and by no means a necessity of life.