I dont know much about metamask but i do using myetherwallet for a long time and i do think its one of the best wallet to store your altcoin and seems like its pretty much okay and safe for me.
It's literally the best one, most of bounty campaigns requires MEW, also it's user friendly and the dev team is really good (even after the split).
The matter is that for today it is the checked up resources and gives all opportunities on safety for the user. I, too, all my time, since I am engaged in crypto currency, using only myetherwallet. At the same time a very pleasant and convenient functional, Combined with very high quality protection.