The dual and triple are more or less the same amp except for the wattage they output. There is also a Single Rectifier. I prefer the triple to the duel although i own a dual rec roadster. All 3 amps use 6L6 power tubes, but basically here's how you break it down:
Single Rec 50 Watts
Dual Red (DR) 100 Watts
Triple Rec (TR) 150 Watts
Now each recto has some different models except the triples (atleast to my knowledge). The Roadster, Road King, Maverick, and Tremoverb are different models of the DR which have differen features from the standard DR. The Tremoverb has tremolo and reverb and has a darker voicing on the gain than a standard DR. The Road King is the king of all rectos as it has tons of extra functionaility. it has progressive tube linkage that allows you to use 6L6 or EL34 power tubes or a combination of both. It also has a ton of features that would be too much to type but check out the mesa site if it sounds interesting to you. The Roadster is somewhat like a watered down Road King without the progressive linkage and some other features but still ckock full of goodness. The Maverick was the least Recto of the Recto family in my opinion. reminded me more of the Nomad and/or the newer Lone Star. The single recs also have a Rectoverb model which is like the standard Single rec but with reverb and a slightly different gain voicing. The Tremoverb, Rectoverb, Roadster, and Road King all come in head and combo versions.
The DR and TR have gone through some changes over the years going from 2 to 3 channels (the two channels sound the best to my ears). The Road King and the Roadster both have four channels. Ok so enough with the rectos.
The Stilletto is basically Mesa's answer to the british or "Marshall" tone but with more Mesa characteristics. I look at it as a more modern Marshall with more features and a better sound. It uses EL34s instead of the 6L6s which gives it more of that british style of gain. Awesome all around amp and to me a prefect compliment to the recto family.
Hope that gives you some what of a start. I've been playing Mesa religiously for over 8 years now and gone through almost all the different models i could get my hands on (TR 3 channel, DR Tremoverb, DR Roadster, Mark IV long head, Redtoverb, Triaxis/2:90, F50, and DR Maverick), but in know way do I compare to the pool of knowledge of this fourm.
