It all depends on one's risk appetite and investment horizon.
Usually small caps and mids caps are more volatile and offer a higher risk-reward ratio.
Profits as well as losses are greater in small caps.
Small caps and mid caps may be a better option for a short term trader who is playing leveraged capital. The movement in bigger stocks is usually slow and this makes them unexciting for traders.
For an investor size should not matter. The more important factors for an investor are growth prospects of a company and valuations.
As an investor I always prefer to stay with stocks that are leaders in their respective industries. e.g. I am invested in Info Edge India Ltd. The company is hardly a midcap , but it is the leader in it's industry.
I feel to make a good profit we should steer clear of stocks with a high Market Cap...as a high market cap means the number of shares floated in the market are high...such shares usually have a strong supply side and it is difficult for demand to overtake the supply unless there is some big news event...so we should choose stocks with low MCap