RE: TRX 2.5R vs. HPI S-25?
All I know is the Savage S-25 (RTR version) is reviewed in the brand new RCCA. They liked it, but it maxxed out @ 34mph, and that was with a lot of massaging. They said that it needs more hp....well, for those who care about top speed it does!! Ths SS version of the same engine ekes out a LITTLE more juice, but it's pretty clear to me that the Savage is WAAY slower than the Maxx or Revo outta the box.
Some say the Traxxas 2.5 is fussy, but IMO, MOST high-performance nitros are fussy, and I've been fine with mine.
This comparison isn't fair to either truck, as they are so fundementally different. And really, as you get into it, you WILL probably upgrade engines on EITHER truck after you wear the first one's sleeve & piston out. And if you figure that in, the Savage actually gives you a lot more engine options in a wide price range (.21s-.28s), where the Revo will only take Maxx-ready engines (Fantom & Sirio .18s, probably the new mid-block .21 Picco variants.
So as you choose, stick to the trucks more than the engines when comparing.
And you REALLY should add the Losi LST to your list. I think that's gonna be the best truck on the market (faster & WAAY more sophisticated than the Savage and more rugged than the Revo). The Savage SS & S-25s are minor evolutions of a 4-5 year old design, where the Revo & LST are both 'clean-slate' trucks that have too many features & advantages to list!!