Ice Type It's pretty cool and can take down Dragon types while also holding up well against its weaknesses.
I liked to keep Gen I rotation with at least two of the following.
Dewgong
Cloyster
Articuno
Lapras
Jynx (wasn't Ice type at the time, but had Ice attacks)
Vaporeon (not Ice type but has Ice attacks)
I like Dragon Type and Flying Type Pokemon. But, they're weakness is one of the easiest to obtain, Ice. Almost all Water Type Pokemon can learn an Ice type moves.