If Trevor Hoffman gets into the Hall of Fame, whats the argument against John Franco? Lee Smith? Troy Percival? That combined with his fascinating ability to blow anything resembling an important game makes him a pretty easy "no." for me. I don't even think he's the second best of his era.

[1] Mo is obviously the best, thats not even up for discussion. But as far as second best over the past 15 years I absolutely think you can make a very strong case for Hoffman, who do you want to put ahead of him? Wagner?

Wagner.

Career ERA: #2 of all active players (Rivera = #1)
Career WHIP: # 7 all-time, # 2 active players (Rivera = #3, #1)
Career Hits/9 IP: #7 all time, #2 active (Rivera, #6, #1)
Career K/9 IP: # 5 all time, # 2 active (Woods, #2, #1; Rivera #25, #9)
Games played: # 1 active, # 9 all time
Saves: #1 active, # 1 all time
Adjusted ERA+ : # 3 active, #14 all time
Career Win Probability Added: # 3 active, #19 all time
Career Save%: 89% (Rivera: 89%)

Easily the second best closer of the "closer era." Comparisons to Troy Percival (e.g.) are laughable.

Should Hoffman be in the HoF? That depends largely on how one values the closer "position." If one sets the cutoff at the best of all time (Rivera), then no. Any lower standard and Hoffman pretty much has to make the cut.

[3] Wagner based on which objective measure: his worse ERA, his lower save %, or his much worse post season numbers?

I like Win Probability Added as a statistic for a closer. Other stats don't factor in the clutchiness of his appearances. And blown saves are going to be pretty heavily penalized. It's also a good way to show that closers (really good ones) actually are as valuable as starters, as Hoffman's rank does.
So I'd vote for him.

If Mo plays two more years as planned he easily takes the all time saves record which would be awesome in my book! He needs 42 to tie.

[7] Yep. Barring injury (make sign of the cross, knock on wood, etc.) he'll pass Hoffman with ease. The only question is whether he does it next year (slim chance) or 2012.

[6] I don't know enough the guts of the stat, though I get what it is supposed to reflect...and I was surprised to see how high Hoffman ranked all-time including both starters and relievers (top 20).

[8] For a closer, it's quite transparent, since he usually pitches just one inning. You look at the team's chance of winning when he enters, and when he's done. He gets credit (or blame) for the difference. So when "Mo needs work" and he pitches with a four run lead, he gets almost no credit (maybe .02 of a W), but when he holds a one run lead he gets about .15 credit. Entering the ninth with a two run lead and losing would cost a closer about .9.

[9] So it's based on historical data (i.e., win probability). But chronological range is chosen? Or do players' totals change slightly over time as win probabilities vary over time?

[10] Oh, good question. I don't know. I would think that for each appearance they'd use data from a chronological range around that appearance.

I lived in SD for a couple years and a native commented on how few of Hoff's SV were of the "pressure" variety. I guess this skirts the "clutchiness" tightrope, but it did seem, when watching regularly, that Bochy gave him the lion's share of cupcake opportunities. That could be a result of fine managing as well though. As a West coaster, I can tell you that his entrance usually meant it was over and last night's AM radio host (FP Santagelo and guest Rich Aurillia) spoke highly of his transition/adaptation to the loss of his mph late in the career and how he overcame that by location, arm angle and mixing it up. You know, pitching. Something to be asid for that as well, IMO. Personally, I wouldn't have a problem with him getting in the HOF. He could be Mo's setup man in the GOAT lineup dreams.