I hope you are investing in ELSS to save tax and not for any other reason. Also understand that ELSS (equity linked savings scheme) does not allow you to withdraw money for the first three years no matter how badly you need it.
I persoanlly dont like reliance brand but Reliance ELSS fund (G) is one of the best funds available in the market. Your choice of fudns are very good.
SBI Magnum Tax gain,
Reliance Tax saver
Principal Personal Tax saver.
Invest in all of them equally.
Eqauity based Mutual funds invests in shares of a companies. The average size of the companies in which a fund invest can be diffrent.
Large cap are companies of very large size. In some domains they have the advantage of cost effectiveness because of their scale of operations, being leader in the market with better market share etc. But the shares of these companies are also highly priced. Usually market trust these companies to earn more for them. Companies that are valued above 3000 crores can be termed as large caps (may be around 200 best companies in India..)
Mid cap are companies that are not very big, yet no small fish. Some of them are market leader in their own domains, but they attend to some niche markets. There are too many companies to choose from (at least 2000 companies in this range) and mutual fund managers work hard to analyze each company and asses its potential and then invest some of the best companies. But most of the stocks are not very popular and when the stock market fails there are very few buyers for this kind of stocks and they just drop value.
Small caps: now you know what they are.
There are some penny stocks as well. They are probably the most intresting in stock market. but mutual funds usually cannot invest much in small cap and penny stocks.