So far after testing Reno, Forgotten Torch, and Jeweled Scarab, I have been most impressed with Jewelled Scarab.
Reno is good, and has that whoa wow effect, but in handlock people are already playing around Moltens because they already know about Molten Shields Up and Molten Back From the Junk Heap so they're already playing around your super secret tech. The archetypes that frequently were forced to go with the "knock him down to 4 and pray he doesn't have moltens or enough support" seem to be less prevalent right now. Reno might be somewhat viable in that deck, but if he is, he is borderline, not a supplier of a lot more power for the archetype.
Forgotten Torch had the appeal of being the 6th burn spell for an aggressive mechmage that wants to finish the game after losing board control from an aggressive start. Unfortunately Mechmage is awful right now, the only deck it can beat is maybe Druid. And Mechmage is forced to do a poor imitation of the opponent and extend into the long game more to adapt to its bad matchups right now, playing Dr. Boom to try to win against Paladin by drawing one of your Doctors while he draws none of his 3 (lol), running Piloted Sky Golem to try to continue going toe to toe with fat late game threats from a dragon priest that's not going to give you an early kill, and running Antonidas for similar reasons. So running the 5th and 6th burn spells don't help with that.. if anything, it's a wonder Frostbolt can stay in.
Tempomage can't possibly care about the Torch at all. With Spellslinger and Mechanical Yeti supplying mana outlets to your hand in addition to the draw you are already running, you'll never need to play a card that mana inefficient.
Freezemage might be pretty decent right now, but it probably doesn't need the Torch. I couldn't seem to play it on my opponent's face before playing Alex because that would be pointless, and I didn't encounter a lot of board states where I could use it as a removal and feel ok about the amount of damage I would be taking that turn. Nobody plays 4/3's or 3/3's you want to kill.
Scarab's been good to me though. Since King's Elek was printed in TGT and Flare was rescuscittated in TGT, Midhunter has had plenty of cards in hand a lot of the time, so you'd think Hunter wouldn't need more and Scarab wouldn't be good. But the proliferation of these ways to draw cards lets Hunter run lots of two drops with impunity right now. The drawback to spamming 2 drops is supposed to be that you'll run out of cards, but between Webspinner, King's Elekk, and Flare, and Tracking's even available, that's not really a concern. So if you cram the Scarab into a list that already has lots of 2 drops, you won't have to play him on turn 2 if you draw him early, you'll probably have a 2/3/4 curve already. So just leave him in your hand. But if you DO have a troublesome 2/2/4 curve in your hand, you can play him, playing him is almost certainly better than playing a 2 drop on turn 2 and being forced to play a 2 drop turn 3. The only situation he's gonna be bad is if you draw a 3/4/5 curve, you cut a croc for him, it turned out he was your only turn 2 play, and look you didn't even need help finding a 3 drop. But that's very unlikely because Hunters can get away with jamming their lists with 2 drops right now as I mentioned.
I still would only run 1. It is a special effect you only expect to need about once per game. But I think it's a nifty card.