Ask HN: Web App or mobile native app?

I am working on an idea and plan to put out a webapp. I feel it is a fun app and am having real hopes for it to be popular. However, I am in a predicament. Should I just build a web app and put it out or wait until I build a phone app as well ? The reason is I don't know how to build phone app, but if I do a webapp, someone could do something similar and beat me easily on execution. I am over the days when I thought idea mean much - but it simply is that I am scared of lot more talented phone developers who could spin similar app over few weekends. Appreciate any inputs or any anecdotal experience.