Why are you guys talking about aluminum? The ToP is steel. As nice as your bike is, I'll tell you I don't want it. No offense, I like my TOP:Wow there is a $hitload of ignorant statements in about 60% of this thread.
OP I will set you straight. First off the Mob is made from TrueTemper SuperTherm tubing which is custom drawn and butted specifically for S&M Bikes. S&M welds the Mob in the US using US manufactured high end $$ tubing. S&M is very well known for producing some of the best CrMo frames on the market.
The Mob has drilled holes for a Gyro install, a chainstay brace that is actually a beer bottle opener, an integrated seat clamp and a few litle differences. Available in horizontal or vertical dropouts and with or without ISCG tabs.
The Riot has the same geometry as the Mob but is made from a less expensive tube set and is welded overseas (not by S&M). The Riot comes in only 2 sizes and horizontal drops only as opposed to the Mob (5 frame sizes and vertical or horizontal drops) so production costs are less overall. Hence the $200 difference.The Riot uses a standard clamp designed for a standard 27.2mm frame. Get a Surly MTB clamp.
The Mob is just under a 1/2 pound lighter than the Riot but the real difference is the feel of the frame. I owned a Riot and then swapped to a Mob and there is a BIG difference in feel. The bike handles better and feels much more forgiving than the Riot did.
Now both of them compared to the TOP is a world of difference in frame feel. An aluminum frame is stiffer than a CrMo frame as the tubing wall thickness is smaller but the diameter of the tube is usually larger than a steel tube. This creats a stiffer frame overall. As far as weight the older frames were over 6lbs but the new 08' weight is now under 6lbs (claimed 5.6 but I think more like 5.9). There new design is terrific and they really cleaned up the geometry.
A couple things to consider are the BB height, chainstay length, head angle and overall wheel base of the complete build. Also the new TOP uses a Spanish BB so you have to go with a Spanish BB set-up for the cranks. No big deal but just different than the Euro BB on the Mob/Riot.
As far as the steel vs. aluminum argument different people like different characteristics. For me riding park and DJ I find that the CrMo is just a better frame material. It does not cause as much shock to the wrists and body compared to aluminum. In addition Aluminum frames will eventually weaken and break at some point. That is just a fact with Aluminum. Sure it may never happen in the time you own a bike, but I build my bikes to last over 5 years. I would not want to be riding any aluminum HT past 5 years regardless of manufacturer.
So in the end either frame is absolutely the best for each material type in my opinion. I have owned 4 different (still own 2) Transition frames and they are a tremendous company to deal with. I have talked to and worked with Keven and Kyle over 20 times for different frames, parts, questions, etc. I have had the same experience with Mondo at BlkMrkt. He knows his stuff and is a great resource. Really either way you go you can't go wrong.
Now comes the swing pics. Tell me you don't want this machine:
Not complete without an action shot...
Just a reminder, I happen to have a MOB, just hang'n out, waiting for a new owner (IT COULD BE YOU!).
My name is Jon, I'll be here all week.