The Fireball has shared eq for both channels, so that's a downside.

The mesa has three channels, separate EQ for each; but horrible clean channel.
Personally I would take the Dual. With a nice chorus, the clean channel is very usable. Just don't expect Fender-y cleans.
Either way, you gotta try them both out extensively. Dont just take our word for it, ya know.

Id say Dual. Just cause Ive got a Triple and know it inside and out. I havnt had much time on the Fireball.
Check out some audio clips, if you can't try them out. Something like this is truely subjective
1981 Marshall JCM800 2203
Mesa Boogie Tripple Rectifier 2 Channel
Avatar G412 4x12 Vintage 30s
Sobbat Drive Breaker 1
I like darker tones so..... yeah you know....... Recto
Tone is all ...... well probably 75%, in your fingers.
The rest depends on your wallet's thickness !!

Keep the faith, baby!!