RE: HPI E-Savage vs. Traxxas E-Maxx
I had this same question a year ago. I did a LOT of research on RCU and other forums, contacting people that had owned both. The biggest advantage of the E-Maxx is parts availability. Every LHS carries parts, as well as almost every online store. The E-Maxx is also quite a bit bigger than the E-Savage. The E-Maxx's tranny can take BL easily as it's quite strong. The resounding advice from the owners of both was...drum roll...E-Savage. While the E-Maxx has a stronger tranny, all the owners of both trucks had lots of breakages with parts, particularly the shock towers. You can upgrade those though, but they said they broke other parts when they did (it just moves the weak link down the chain). Of course there will be those that are quite durable, but my research revealed that the E-Maxx does tend to have weaker plastic parts. This is somewhat offset by the fact that parts are readily availabe and cheap.
While the E-Savage has a weaker tranny, diffs, and axles...the axles can be replaced with the Maxx ones and the diffs when shimmed properly work fine with BL setups as evidenced by numerous E-Sav owners with BL setups (see e-savage.com). The stock axles tend to break when landing off a jump with lots of throttle. I've made a concious effort to not do that, tho I've occasionally done it at full throttle and not had a breakage yet, but I have spare Maxx axles already just in case. I've smashed my E-Sav head-on at full speed into boulders with no problems. It's a super tough truck. The choice is ultimately yours, but I'm very happy I chose the E-Sav as I don't have much spare time and while I don't mind wrenching, I prefer to use my limited time playing.
Oh and yes, E-Maxx and T-Maxx parts are interchangeable. E-Savage and nitro Savage parts are NOT interchangeable. Savage Flux and Savage parts are interchangeable (Flux uses a Savage X chassis and hubs/wheels from XL, and other mix of nitro savage parts). The Flux would be a super awesome monster! It runs a Neu motor and a MMM, plus it's bigger than both E-Maxx and E-Sav. It also costs more than both of course. If you can afford it, skip the other two and go straight for the Savage Flux!