With all commercially available conversion tools, converting fonts between scalable formats almost always results in a font inferior to the original. First off, any font that's converted uses a converting algorithm which will make an exact copy at best. Because no currently available converter even comes close to copying faithfully the manual tweaks and hinting in a font file, you often end up with poor screen fonts and poor output. The only reason that printed output from the converted font looks markedly better than the screen font is that the printed output is at a higher resolution. The converter achieves better results on the higher resolutions because hinting is less important at higher resolutions.
Screen fonts are incredibly complex to make well.
You have very few pixels to represent a very aesthetic and distinct design. And that's why most fonts look similar at 10pt, unless they're hand hinted by typograhers. Also, the conversion programs may have made the appearance worse at some sizes than others. The font may or may not have the correct character sets in it. The TT font file may or may not have all the tables necessary.