TNG is so heavily weighed down with 80's ideology it's become very dated. DS9 has real characters who are flawed and much more believable - much more like Kirk and Co. than TNG...whose characters are all so tediously 'evolved'.
Not all good dramas require it's main character to be at each other's throats. The characters constant bitching at each other in NuBSG was one of its biggest flaws for me. At some point it turns into a soap opera, which thankfully DS9 didn't reach.
The TNG cast not fighting all the time didn't mean the characters was evolved, they were just being professionals.