Ceilings are not easy to get right, and texture is not a substitute for good workmanship. Texture will hide minor defects by difusing shadows and light across a flat surface just enough so minor imperfections are not noticeable. If joints are improperly filled or not sanded, there will be a pattern of imperfection that you will see right away. The effect is worse if lighting is close to the ceiling and shines across the seams (ceiling fixtures, sconces, and fans), and is least noticeable if the light source is from below (daylight and table lamps). A poor tape job just seems to jump out at me, and it affects my impression of the quality of the whole place.
I recommend that the time be spent to properly fill and sand the joints and nail holes before you paint or texture. Once you have covered over the problems with paint or texture, they are much harder to fix.