I was looking for an online wallet because last time I installed a altcoin wallet, it took month to sync and killed my system performance altogether.
This was due to the fact that you had installed a full node (needs to download/sync/process the whole blockchain).
Light-weight clients (electrum) do connect to a server which does provide the relevant information (balance / transactions of your addresses).
If there is any other safe option online?
Also, unless you really know how to protect your device/connection, there aren't any safe online wallet.
Even if you know how to protect your device, and even if you do know a lot about networks it is not guaranteed that an online wallet is safe.
The thing with online wallets is that at one point you have to rely on the web wallets server.
Imagine the following case:
Your PC is completely secured from any malware (not possible, but lets assume it).
You visit blockchain.info or any other web wallet, check whether you have entered the URL correctly (maybe use a bookmark) and verify the SSL certificate.
You then enter your credentials. A few seconds later.. everything gone.
What happened? Were you not cautious enough? No. An attacker just had a valid SSL certificate for this site issued by a CA which had a security breach.
While you were thinking you were on the online wallets server, you got directed to the attackers server (which does show a valid certificate for the online-wallets URL). You basically just got phished.
There is not a lot you could have done in this case. You might have checked whether the CA from the SSL certificate does match the previously mentioned CA and keep a list.. But that would be a really paranoid way.
Thats just one example. Online wallets do have way more attack vectors than traditional desktop-/mobile- wallets have.
You can be the most security-concerned person, but you won't never be able to keep an online wallet fully secured with no possibility of theft, ever.