Good for RF sims. It's free compared to ADS which is NOT. You can use LTSPICE for some kinds of e.g. transmission line models but it doesn't have things like t

Good for RF sims. It's free compared to ADS which is NOT. You can use LTSPICE for some kinds of e.g. transmission line models but it doesn't have things like the Smith chart built in. You also can use Qucs for modeling things you'd normally use SPICE for but the library isn't there, so it's not worth the trouble. Basically, two different tools for completely different sets of problems.