I would like to hear your advice which should I start for better profit. Affiliate marketing or Google adsense?
Well profit depends on your skill, knowledge, luck and determination. Lots of determination. Blood, sweat & tears. Also the niche or product you choose to promote to how you promote it.
How to invest less but earn more from one of 2 these fields.
Neither require any monetary investment as its free to apply and be accepted for Google Adsense and there are plenty free to join affiliates with products/offers/services etc to promote.
Both will require investing a lot of time and hard work on your behalf though if you are to make anything worth making.
But you cannot earn more or less from either. Both pay different amounts depending on how well you're doing with it, what you're promoting, what the CPC/EPM or cut is.
There are no shortcuts unless you come up with something new or cool or manage to get your site ranking 1st for something worth ranking 1st for.
And these days, that ain't easy, especially for new sites.
Sorry if that's not what you wanted to hear but its the truth.
What you put in, you get out.