For me, There is nothing to make a comparison between bitcoin and PayPal. Both are necessary depending on the users' needs. PayPal uses there interface to exchange fiat across borders and bitcoin uses it's own digital currency as payment currency and payment interface through exchanges as well. These systems are not competitors to each other.
Yeah if you think about it, Paypal is already a pretty dated system in terms of usability. I can easily see bitcoin or other payments blockchains far surpasing the value of paypal and also the volume of transactions, payments are increasingly natively digital now.