"Best"? That is such an over used term.
It is better to evaluate aircraft based on which role you want it to fill. Likewise, it is hard to place the title of "best" on anything, even in a certain role. In terms of delivering ordnance the Tu-2 is a splendid platform. It carries well enough ordnance, it climbs well, and flies fast. However, it is limited defensively and on range respectively in comparison. No matter how you try and cut it, the Tu-2 is medium bomber. It can't bring the hurt to the strategic targets like a B17, B24, Lancaster, or B29. Or even the Ju88. Sure, it can haul triple 1000kg bombs (2200lbs), but there goes that climb and speed that was so fondly mentioned earlier. Otherwise, it can carry 4/500kg bombs which in itself is respectable.
Where the Tu-2 excels is in the short or medium range strikes in which the goal is to hit hard and get out. If it is used in conjunction with heavy fighters or other attack aircraft it works nicely. The pair of 20mm is a nice addition and can polish off any last few buildings or ack guns.
It is certainly an aircraft unique unto itself. Is it best at anything? Nah. It is good at a lot of things? Indeed it is.