you could maybe start by looking at this thread :-
Hpi Pro 4
Oh and this one :-
Now correct me if i'm wrong but i think the comparisons on the HPI thread start on the first page ??
Now since you don't seem to be bothered to do the research yourself...............
TC3 is up for replacement, rumours are in time for the worlds !!
HPI is the new car on the block of the 2.It shares many similarities with the TC3 but is not up for replacement just yet !!
TC3 is very established with many sources for both spares and set-up help although the HPI is well on it's way now !!
I'd say get a barracuda R3 though, as it has the best bits of both cars IMHO. But has better reliability than either and that just has to be a good thing.
No flames dude