I don’t think anyone enjoys life all the time, theists and atheists alike are all burdened with the same problems; health, mortality, loss, ageing etc. Suffering is universal, however a potential difference could be argued between a theist’s capacity to cope with suffering and that of an atheist.
I would be inclined to think, however that a theist is not necessarily equipped to deal with suffering any better than an atheist, in fact I would argue the opposite. A theist’s view point is one of eternity, that we continue beyond this life in eternal paradise, or damnation. It could be argued that this tendency towards idyllic permanence is in conflict with reality. Nothing lasts forever, and acknowledgement of this fact reduces suffering because when one is faced with loss or change one can reflect upon the impermanence of things and understand that it’s part of the way things are. Could it be that one who’s mindset is inclined towards permanence may have difficulty accepting the truth of impermanence?
I think the counter argument to this would be that theism gives one the strength to rise above worldly troubles, but I think that this is often not the case. Theists will often question their faith when faced with suffering, rather that use it to escape suffering. This adds a whole other level of suffering to the mix, not only is one suffering problems, one also has questions rising about their fundamental view of reality – which in itself can be classed as a kind of suffering. I think theists often doubt their faith in times of trouble, then this will just reinforce their faith later on when things become more settled. Problems generally sort themselves out in time, but a theist would be inclined to believe that this was God helping them out, thus reinforcing their faith. So they end up with these stories of how they were faced with really hard times and even doubted the existence of God, but later everything was okay, so God proved himself to me by directly helping deal with my suffering.
I don’t think there are many honest theists who wouldn’t admit to having occasions in which they have doubted their faith, this is a problem that atheists are never faced with. An atheist would be less inclined to doubt their fundamental views on reality when faced with suffering (I say less inclined because I am open to the plausibility that an atheist might be converted to theism when faced with suffering), they would merely understand that it is part of life, and therefore in my opinion suffer less as a result.
An imagined relationship with a omnipotent, omniscient, omnipresent being would be a psychologically bizarre relationship. As with most relationships they cause at times a certain degree of suffering. But nobody has an all seeing, all powerful, all knowing girlfriend. Imagine the nightmare that would be! If this girlfriend could read your thoughts, you would suffer immensely if, say you lusted after another woman, more so than you would if you did so, but managed to keep those thoughts to yourself (without acting upon them!). There would undoubtedly be a great deal of psychological torment in such a relationship. A theist would have similar problems in their relationship to God.
God wouldn’t like you thinking about other religions, or questioning his power. He doesn’t like sexual urges. And he promises eternal suffering as punishment for turning your back on him. It’s analogous to the worst kind of abusive and controlling relationship imaginable. Like a wife who can’t even think of hating her controlling and abusive husband because he can read her mind and he will torture her if she thinks anything bad about him.
I would say that theism, (at least how I have defined it here) is more of a cause for suffering than a relief. There are many psychological issues that theists would have to face because of their faith in God, this is a whole load of issues that people without faith never have to face.
An atheist would strive to find meaning and understanding in life. Understanding suffering for what it is, and knowing that the same principle that so often causes suffering, also takes it away eventually. Impermanence.