have thought of something what will be best/fast in defence and arround the net a 3U racket whit a lower balance point like the kason twister f9 bp 295mm or a more HH racket like the volric 70 305mm ind 4U and what will give the best smash? the racket i say is just a exeampel
Generally, the lighter the racquet the faster it is at the net. Since you only really use your wrist and forearm at the net, you need something you can accelerate easily. So even to headlight and reasonably low weight. Again this will be down to personal preference. Some people may find that head heavy racquets works best for them at the net.
Same with smashing. Even to headheavy are best for smashing. But it depends on a lot of things such as your technique, physique and personal preferences. Even if you spend most of your time at the back smashing, there will be instances where you will need to play net and midcourt, so to go for a racquet that is solely good for one thing seems a little daft.
For doubles, most people would choose a headlight to even balance racquet and most would select a 3U weight.
imo you will notice balance point more than overall racket weight. e.g. VT80 is heavy to swing but is actually quite a light racket. head light rackets are very easy to move but in terms of weight are not that much lighter than head heavy rackets.
you can smash well with either. depends on your smash technique. i.e. short/long swing, fast/slow swing etc.
around the net, it depends what your doing. you can still move a hh racket quickly to block/net shot but you'll need more 'torque' to flick/tap without an arm swing.
My experience with 3U balanced and 4U head heavy is that the 4U feels more powerful but less agile than the 3U. There is no perfect racket and you really have to see what's more important to you, or what your weaknesses are, and choose one to compensate them.