main altcoins advantages are:
1) Built in VM, allowing to make complicated smart contracts (allowing transparent ICOs, DEX, games, etc etc)
2) Fast transactions = high TPS output. You don't need to wait 5-180 mins for just 1 BTC confirmation (ok, it's 10 min average blocktime

)
3) Anonymity code implementation, built in (Monero, Zcash etc)
Good altcoin is developing much faster than BTC IMO...