Blue wallet supports only bitcoin so if you import the trust wallet by entering the phrases, how will it import the altcoins stored in the trust wallet?
It won't show the altcoins. Both wallets generate BIP39-compatible seeds, but only one is a multicurrency wallet while the other isn't.
Or it will only show your bitcoin present in trust wallet?
Assuming both wallets use the same derivation paths, and I think they do, only your bitcoin will be recovered.
My second question, Electurm or Blue Wallet, which one you think is better?
I agree with LoyceV on this one. I use Electrum myself, but only the desktop version. I don't like the mobile version as it lacks important features compared to the desktop one. Blue Wallet on mobile has more advanced options than its Electrum counterpart. It also looks and feels better.