online ewallet safe to use? or most better bitcoin use on local pc?
It's off-topic, but online wallets are as safe as the owner is trustworthy and competent. People here will usually yell "trust nobody!" by default, but it's not as simple. In some areas I trust my own skills less than those of certain individuals behind certain companies. You need to decide for yourself. Just keep in mind that some online wallets fully own and control (and risk) the private keys to your coins, whereas some services store private keys on your local machine, and only take care of the blockchain management for you.
If you decide to run a local "full" client, plan on leaving that PC on all the time, plan on waiting up to several days for the initial sync, and plan on having lots of disk space.