DAI can also be frozen, but much more difficult than all other stable coins. DAI freezing requires a vote by MKR holders. Now, I dont know, whether government can bypass this and just enforce the freeze on DAI.
Still, DAI is the most safest stablecoin compared to other stablecoins (e.g. USDT, USDC, TrueUSD etc)
I think that most people still use USDT because it's pairs have most trading volume. I would definitely rather use DAI but some tokens don't have a pair with DAI and those tokens that can be traded for DAI doesn't have nearly the same volume as USDT. Here I'm talking about trading on Binance, not on Uniswap or similar DEXes.