Lets be fair: Glavine had one championship
Cy Youngs: Glavine 2, Mussina 0
20 win seasons: Glavine 5, Mussina 0
AS: Glavine 10, Mussina 5
And remember that Glavine pitched on the same team, never mind same league, as Greg Maddux in his prime. And John Smoltz.
I'm not averse to putting Glavine in the HOF. In regards to the Cy Young and All-Star Game appearances -- I'd put more stock in those categories if both Mussina and Glavine pitched in the same league (not to take away anything from Glavine).
And, to me (*sigh*) the Wins are tricky too. Mussina won 16 or more games 8 times in his career. Glavine won 16 or more games 8 times in his career. Mussina missed the 20 Win mark by 2 games or less 5 times in his career -- the same number of 20 Win Seasons as Glavine.
If Mussina can get to 300 Wins, which might be difficult as he'll have to give 4 more seasons (which incidentally is the number of seasons Glavine's got on him), then I think he's a HOF.