The more OTM the smaller the delta, but also the smaller the premium.. So the real factor of interest is how much of a percent of the premium the delta is.. For instance, if the premium is 2$ and the delta is 0.3, then if the stock rises with 1$, the option will rise with 30cents, which is 15% of the premium.. I took some easy numbers to avoid having to dig up my calculator, but you can easily calculate this percentage for all the options at all strike prices and expiries..
Well, I didn't do it for all, but sampled some 20 different ones, and I found that the more OTM the better the leverage..
Or IOW, if you have 5000$ to play with, put it all in on the most OTM ones.. And when the strike price is approached, roll up to a higher strike.. Increases your leverage again, and since they are cheaper will leave you some cash to further pay with..
And since you're living in Belgium, you don't have to worry about taxes.. (if you are taxed in Belgium, that is..)