They worked well as both...Some guys have the charisma and ability to sell to the audience that they can successfully be believed as both, like HHH & HBK or Ric Flair & Sting. Some wrestlers just dont for whatever reason have the charisma to connect as well as "friends" as opposed to "enemies"... See Edge & John Cena, Randy Orton & Cena or Orton & HHH, or go old school with Flair & Hogan.
Savage and Hogan were very believable in both contexts, with the underlying competitiveness or resentment from their early feuds circa 1986-89 always somewhere just under the surface. My only gripe about their feuds was Savage was never allowed to come out on top, despite the fact they had multiple runs against each other in both WWE & WCW and Savage was a pretty big name in the industry. It's hard to count the Top 5 Wrestlers nationally in the 80s without Savage and I would dare say he was in the Top 5, or at least safely in the Top 10, for the decade of the 90s, something no one else who was that big in the 80s could do other than Hogan & Flair.
I do feel WCW dropped the ball by having Savage go NwO. There was great potential for an uneasy partnership storyline wise between Savage & Flair (two guys with a long, nasty history vs each other) as the natural enemies of Hogan and the NwO, along with Sting they could have been a very entertaining opposing force to Hollywood Hogan, the two guys who most rivaled him in terms of in ring success and national prominence and the one true good guy/hero type who wasnt selling out like Hogan did. With all their past storylines of their own between them and their in ring ability they could have been a terific force to oppose the NwO. Having Savage join the faction unessarily weakened WCW but he was also grossly underused, basically a mid teer guy for the most part, his one brief spotlight moment coming right before his injury lay off when he was allowed to win the World Title only to immediately drop it back to Hogan. Then we never got a good payoff between Savage and Hogan or Savage and Nash once he returned. Like much of WCW from this time period, a ton of potentially great stuff that only lived up to about half of it's potential due to poor booking.