They both have advantages and disadvantages but altcoin is the major one having too many problems

For bitcoin
1. Bitcoin is the first of its kind
2. Price stability
3. Better support
4. Better future gurantee

For altcoins
1. Better features like faster transaction fee
2. Cheaper sending fees
3. Low support for many altcoins
4. Atcoins getting born everyday
5. Scams all around altcoins
6. Unsafe for many but yet they have better future