Perfectly agree with Manoj. The 3 head machine is complex because it gives provision to align height, tilt, stroke and azimuth. In 2 head models many of these are fixed. Now that being said, if a 3 head model is misaligned, that would sound bad. But what is the meaning in comparing an impaired 3 head unit to a good 2 head unit. Whether it is a 2 head or 3 head, the owners have to take good care and maintain them. Else they go bad anyway.
To do an honest comparison, all the units have to perform to factory speks, then the 3 head units will outperform the 2 heads in technical performance parameters as well as the listening tests. The difference in playback require good amps and speakers to be evident, but the recording performance can be easily noticed. In addition, the 3 head ones have a lot of features added in like record cal, bias cal that makes a lot of difference to the quality of recordings. Also the head life is much longer for 3 head than 2 heads.