Noise Tool: very fast, but standard signal conditioning circuits only
LTspice: slower, but you can build anything
The Noise Tool is designed to let you build and iterate standard signal conditioning circuits extremely quickly. For example, you tell the noise tool you want a Gain=12 amplifier stage, and it creates the block for you - with the amplifier and appropriate resistors. If you did the same in LTspice, you would have to figure out the resistor values on your own, place them, and wire them up. The Noise Tool simulates on the fly, so you can see the results in real time as you are building. Everything about the Noise Tool lets you iterate quickly. However the Noise Tool is limited to standard signal conditioning circuits. It's not "open world" like LTspice, where you can place anything wherever you want. LTspice also supports more simulations, for example time domain.
The intent is that you iterate with standard circuits in the noise tool - quickly understand how they work and the tradeoffs. Get 80% of your signal conditioning work done. Then export LTspice where you modify those standard circuits to make the custom solution that fits your particular application.
