Before this devoles into the inevitable GT hate-fest, I'll say this: the biggest difference between a pack with GT and a pack without GT is pace and flexibility. GT has defined Ages of tech, and thus resources that can be processed and used. This requires a different overall strategy than a Kitchen Sink pack like Infinity. Some people love it. Some hate it. A lot of both like to argue with one another over their different opinions.
A Kitchen Sink pack like Infinity allows you to jump into and out of any mod in the pack whenever you want (resources willing, of course). Infinity in particular has a number of mods that Resurrection does not, giving it a wider range of cross mod interaction. Mods like EnderIO, Draconic Evolution, Funky Locomotion, and more allow much greater flexibility in builds that doesn't exist (or at least is much more difficult to accomplish) in Resurrection.
Resurrection shines in bringing material management and smart design to the forefront. Because resources are a challenge, a player must consider if the investment being made will be worth it in the long-term, even when considering simple things like wiring choices in the early game. The pace is slower, more methodical, and occasionally you might have to walk a good while to find a resource in need until you can invest in higher tech that might be able to produce that material by processing another ore. Once things get moving, I feel the rest of the pack opens up a bit as there are a few ways to skirt around GT with the other mods. Once I got into it and figured out the pace and basic GT mechanics, I had no problems playing in that sandbox. My friends couldn't get out of the bronze age without swearing obscenities at all that is GT, so now we have an Infinity server. To each their own.
Infinity is a different beast. This pack is recess. There are few rules, and fewer laws. Jumping balls deep into a mod and then abandoning it to go do something else isnt a death sentence here. Using one mod to prop up your entry into other mods is good form here. There are a hundred ways to accomplish a task here; feel free to pick more than one. Where Resurrection is a test of patience and management, Infinity embraces imagination without (or with few) consequences. Again, to each their own.
Moral of the story, try them both and see what you like. The world has opinions. Only yours counts for your happiness.
