Do you think, "Paid Marketing (PPC)" best for promoting online business, If yes, so why works on "Organic Marketing" (SEO)?

No, would be the answer if I think PPC is the best for promoting online businesses. What I think best is a 360 Degree approach. Marketing is the quintessential backbone of any business and we should not limit ourselves with a singular medium or channel.

And moreover integrated online marketing makes business sense too. PPC is a quicker way to traffic to your site but you need to have long term visions too, for which SEO and Social Media plays an important role. As I’ve said in my earlier answers :

Start with a budget allocation of 50% PPC (60% Search,30% Display and10% Remarketing) ,20% Social Paid,10% Social Organic and20% SEO. In the PPC segment target for maximum conversions and in Social go for maximum visibility. As you gradually build up the authority of the website more and more taper yourself from paid to more towards the organic model. In a year time your budget allocation should somehow look like this40% SEO,25% Social Organic,10% Social Paid and25% PPC (40% Search,30% Display and30% Remarketing)

And always go for offline presence if your vertical demands it, as it increases the trust factor which leads to increase in digital conversion.

Promoting an online business in an aggressive market - which require better ROI , i suggest the best methods should be fully focused on SEO  and Community/ Social Network channels - Both Organic and Paid. Always keep PPC less than%. There should be a continuous evaluation on attaining the targets, with different permutation and combination on Paid and Organic. 

You must optimize your website organically for visitors and use Paid marketing later.

If the website is not well optimized and users dont feel comfortable on your pages they will leave and bounce rate will go up.

So before using PPC try attracting users anyway, and the better website, the more user engagement and PPC will have more impact.

Paid Advertising is quicker way to get listed in Google, Bing , etc  its is only recommended for Less competitive Niche & countries like UAE its not too much Costly . If you are going to use in Usa Competition is increasing every month mostly you have to pay more then $20-$30 for a Single click. I always suggest to start both SEO , Paid ads , Invest60 % of budget on SEO ,40 % on paid advertising , get listed quickly with paid ads & work on long term basis using SEO , After you build some visibility in Organic , stop paying for Paid ads ,