Well a mock CAT series could be measured on these two parameters:
1. The proximity of questions in mock to the real thing
i guess TIME AimCAT are pretty good. CL used to be good dont know about how is it now. IMS SimCAT have been known to be ridiculously tough, insanely tougher than CAT. In fact i came across a question just while flipping through one old paper [of a friend's] they had a math question in form of a poem! "hickory-dickery-dock" i said WTF! i mean its a known fact that neither MBA nor IIMs have wanted crazy mathematicians. But i read somewhere on PG itself that last year IMS people got back to senses & 2007 mocks were pretty good.
2. The number of people who are writing
TIME & IMS are the leaders. Dont know the exact numbers though!
So its a toss-up between TIME & IMS, but i'd go with TIME AimCAT. A negative is that they are a little too steep when it comes to price. I mean 5000 [they havent revealed the price of 2008 series] is like over-valued stock

. Agreed, they are good. But they cant damn guarantee how close they can get to real thing. Its only since last 2 years CAT hasnt changed its colors. Who knows we might be in for some shock?!

One more thing: though im not an expert neither i have cracked CAT but i cant understand why people go for two, or even strangely, more mock-CATs. The whole point of a mock CAT is to keep the prep going great guns & seeing where one is standing AFA the real competition goes.What could be done at most is form a group of 2 or at most 3 people who have a good understanding of what is to be discussed: no point in talkin about EVERY question. only that q which was really tricky or was pretty close to real CAT is worth discussing about. AFA the language section,i think all classes are in dark. I mean could they match CAT 2006 language?
Overdoing it may be overkilling. Over-curiosity might just kill the CAT
I will be going for TIME AimCAT btw.