Mini types fit 8.4V and 9.6V. More milliamps (MAh) is better also.
The battery that came with your Kraken is a sub-c 8.4V 1100MAh. I use the stock battery all the time with no problems - I also like the rate of fire.
If you use the larger sub-c type, you're restricted to 8.4V as the 9.6V may be too large and not fit in the stock.
The mini-tamiya connectors are fine IMO, deans just offer a larger connection area which supplies more efficient power to your rifle. If you're not comfortable with changing connector ends, don't.
I've had no problems with my Kraken using the stock wire set, the stock gear box, and the stock battery, but one thing you may want to look into is a smart charger as the wall chargers are usually junk and can destroy batteries even when used properly.