For the xcube, you're going to want build for a bit of resistance for it to read the changes well. Firmware updates helped a lot, but I have gotten funny behavior out of it close to the ends of its operating range.
I'd try to aim between 0.1 & 0.5 ohm cold resistance for TC.
I have experience with the SS, but haven't touched Ti. If you look back through this thread for posts by
@cigatron , he does Ti exclusively, and I've seen a lot of people thanking him for his advice, so there's a place to start.
When you do get SS in, I suggest twisting it, I haven't found an SS yet that isn't improved by a tight twist. I've had good results from twisted 28 ga.
Many people recommend 430 grade SS, and the tcr is good on it, but the base resistance is low, and it's not as amazingly easy to build with like other grades, so I'd recommend 317L or 316L to start with, but wires cheap, sometimes cheaper than shipping, so you may want to order multiple grades and gauges all at once.