Give me your altitude/flight level to within 100 ft every time, as triadic wrote. No matter what phraseology you use, I want accuracy every time because I base separation, particularly in procedural airspace or in the case of mode C failure, on an accurate altitude. Why? Because we assume that, when you are within 300 ft of a level(200ft in RVSM airspace), you are at a level separated from other levels. In the case of a climbing or descending aircraft, the nearest or best 1000 ft level doesn't cut it for me. There's also the small matter of 500ft separation in some airspace where we need the most accurate level you can give.