K, first off I would like to say that @tiedyedvortex review is excellent, but I would like to narrow it down it a bit more after my experience playing this with Rielle "Kit" Peddler: Transhuman. First off, we all now Kit is about early aggression in order to make most of her ability. IMO this gives you 3 options: Gordian Blade, Refractor and Study Guide. You also have Torch and Yog.0, but these builds require more specific combinations in card draw (Test Run+Scavenge or Dinosaurus+Scavenge etc) and those builds are more suited for the late game.
Now for the first 3: Gordian Blade is the most aggressive. You install it and you can run with no problems right away. The downside though is that Gordian Blade has the worst late game sustain and boosting it with recurring credits is less efficient as with Refractor. This is a bridge you have to gap while building your deck.
Refractor is cheap to install massively efficient with it's recurring credits, has great sustain, but requires stealth credits to work. With 3x Cloak, 3x Lockpick and 0-3x Ghost Runner it shouldn't be to hard to see a stealth card early. You are devoting quite a large portion of your deck to make it work, can probably make only one run a turn in the early game, but it leaves you a lot of real credits left to do other stuff. Once you go late game it really starts to pay off.
Study Guide fits in between the two. It gives you early game independence from other cards like Gordian Blade (although a lot more expensive), but once you slot in the right support cards it gives great late game sustain. The cards I'm talking about is Stimhack and Lockpick or Cyberfeeder (you can also use Cloak, but then you need support). Installing Study Guide and then using Stimhack gives you a permanent S3 decoder right of the bat, same S as Yog.0, which is absolutely fine for most early game ICE. Once you get your Lockpick out you can let it grow on recurring credits each turn (even if you don't make a run) or just pay up front. I've had games in which it was S5 by turn 3, making Tollbooth a joke for the rest of the game. Another bit advantage IMO is the fact it doesn't need recurring credits each time you run, so you are perfectly able to make multiple runs without worrying about running out of those and still be as cheap. The Lockpick you are using first to boost it, switches over to helping you break subs.
I would also like to give a special mention to Escher. A card that is nearly forgotten, but fits great in a Study Guide deck. Firing it in the mid-late game can absolutely wreck 1 or 2 servers for multiple turns. It fits Study Guide better than Refractor as it can take more advantage of it in a single turn (Esher + one or two cheap runs, before corp starts rebuilding).
Is Study Guide better than Refractor? IMO it is about the same power level. A Refractor deck is a deck in itself. It makes one run a turn and it does it very well. Study Guide gives you more room to play with. You can go all recurring with it (for strength boost early game, sub breaking late game) or brute force it with pure econ/Stimhack or you can do both.
If I could make a chart for strength over game time then Study Guide will have a same peak as Refractor early game, is weaker mid game and stronger late game. This makes Refractor better for fast advance, but I think Study Guide will be better for against RP or Glacier.