I have a cisco querie?

For anything CCNA or below, Packet Tracer is probably the best. For any routing stuff higher than that (ie: CCNP BSCI), GNS3 is probably your best bet since it can emulate real IOS. I say Packet Tracer is the best for CCNA or under because it supports all the CCNA-centric commands and it cam emulate switches, which GNS3 cannot.