buy an iMac or a PC?

Hello everyone,
Time has come for me to buy a new machine. I have always used PCs at home, work.

I am now toying with the idea, that may be I should get myself an iMac. I guess what’s holding me back is I don’t know anything about Macs, never used them. As a result I am unable to evaluate the specifications .

Also, is it difficult to do upgrades to memory, hard disk extra once I buy it.

So is it better to get a PC or an iMac

Thanks in advance.