Bastante can be an adverb or adjective. whereas suficiente can only be used as an adjective (the adverb is suficientemente).

Their meanings are also somewhat different. Bastante can mean enough, but it can also mean just a large amount or a lot.

He comido bastante. -- I have eaten quite a bit/a lot.

Suficiente usually just means enough.

Tengo suficiente dinero. -- I have enough money.

So while they can be used interchangeably in some cases, they do have distinct meanings and usage.

Hope this helped

x