I think the FBI who holds the worlds biggest bitcoin wallet estimated of 144 bitcoins now a days as they shut down the silk road online drug market place. But i do believe they are not only one holds the biggest wallet because we have many anonymous person containing bitcoins we can not trace there wallet how much.
If you don't know what you're talking about, then please don't. The seized SilkRoad coins have been auctioned off a long time ago, and thus they are back in circulation. They may very well hold a certain numbers of coins from other closed platforms or other cases, but these are neglectable in quantity, and will eventually get auctioned off as well. On top of that, the blockchain is transparent till the extent that everyone can browse through it, and thoroughly analyze it and connect addresses to people in some cases -- there isn't such a thing as anonymity.