At starting many webmasters are confused about using SEO or PPC at start.
But many commercial sites are going good by using mixture of both if you have exact goals.

PPC (Pay Per Click) :
Advantages :
1.You have to pay for your advertisement. You will get instant result.
2.You can stop PPC ads at any time.
3. Great for seasonal time.
4.Though any website dont have good desgin and SERPs still they can earn good money with PPC.

Disadvantages:
1.It may be risky if you dont you bid on right keywords.
2.click fraud can be a problem..

SEO(search engine Optimization):

Advantages :
1.If optimization done correctly, you will get loads of traffic completely free
2. It delivers long term results.
3.no fraud.

Disadvantage:
1.SEO can be very time-consuming.