The weight of the blade itself can be a factor. Lighter table tennis blades can usually be swung more quickly, but heavier blades have more mass to use when hitting the ball. In physics terms, momentum is equal to mass multiplied by velocity, so you should look for the heaviest blade that you can still swing comfortably and quickly - this should give you the best speed when hitting the ball.
The stiffness of the blade refers to the amount of flex or bend the blade has. A stiffer table tennis blade will generally be faster but less spinny than a flexible blade.
The balance of a blade refers to whether the centre of gravity of the blade is closer to the handle or the tip of the head. Loopers and hitters tend to prefer head-heavy blades which help them generate that little bit of extra spin and speed, while blockers and defensive players quite often prefer blades with the centre of gravity towards the handle, which can increase the feeling of control. Bear in mind that the centre of gravity of a table tennis blade can change quite a bit depending on the weight of the rubbers you choose - heavy rubbers will tend to move the centre of gravity out towards the tip of the rackethead.
The general wisdom regarding table tennis blade speed is that faster blades tend to be used by the more aggressive players, and slower blades by the more defensive. Players who use more spin also tend to prefer slower blades, because they believe that a slower blade increases the amount of time the ball is in contact with the rubber, giving them more time to put spin on the ball. Note that this does not mean slow blades necessarily - for example, Timo Boll may use a slower blade than many other professionals - but you can bet it is still pretty fast!
The difference in air resistance between large headed table tennis blades and smaller headed blades is pretty much insignificant, so the main issue of concern here is that larger rackets require more rubber to cover the surface, which makes the racket heavier and also tends to move the centre of gravity of the blade away from the handle.
The choice of handle is usually a matter of your own preference. There are a couple of things to consider though. The rule of thumb is that players with stronger forehands tend to prefer flared handles, possibly because they allow you to get a better grip when executing the forehand stroke. Players with backhands closer in strength to their forehand seem to prefer straight handles, since this usually gives them better flexibility on the backhand stroke. Defenders and combination bat players who twiddle the bat also tend to prefer straight handles, since they are easier to flip.
Besides the standard penhold (both Chinese and Japanese) and shakehand type handles, there are others exotic creations such as the pistol grip blades, and even the V-grip blades. Whether these different handles are fads that will come and go or the start of new styles remains to be seen. They are pretty much unproven at the world level, so I'd probably suggest against using them unless you wish to be an innovator and risk using an inferior handle and grip.
In the last few years, manufacturers have also introduced technologies such as the WRB, VSG, and Senso, which basically hollow out the handle to move the centre of gravity closer to the tip of the table tennis blade. Exotic claims are also made about reducing vibration, increasing touch and feel, etc, but these are best treated with a grain of salt. Try them out and see for yourself whether the reality lives up to the marketing pitch - who knows, maybe it just might!