below the answers according to my experience with NanoSim, HSIM and Mach-TA.
* Big digital design: NanoSim seems to be better than other two.
* all kind of memories: HSIM is absolutely the best one and judging from other people experiences HSIM doesn't have rivals;
* Big D + small A: it depends of design complexity (mostly the complexity of the analog part). In my opinion the best thing is to co-simulate HSIM with NCSim. It's a very robust and stable solution.
* mostly analog: HSIM is the best one and judging from other people experiences, other mature FastSPICE tools aren't at HSIM's level.
* RF: unfortunately I haven't had any experience on RF design.
Taking in consideration various evalutions I saw and the rumors from EDA world:
- Cadence UltraSim is less performant than HSIM on analog & mixed-signal;
- Nascentric doesn't have still a stable, robust and large spectrum product;
- ADiT: is on going the phase of integratin within Mentor ADVance-MS environment. I'll test it.