what are the merits and demerits of different types of political party system, i.e, one party, bi party and multi party systems?

advantage of political parties is that they give the voters a versatile choise for them to select  there leader.

its demerit is that in political competition people are being crushed, and the leader srather than to concentrate on meeting the demand of public are readyto blame each other,forgetting the need of people who elected them