On SPICE simulation
For many yeares I have been ussing a paid-for circuit simulator, part of the Proteus package from Labcenter in the UK. In 2017 I decided to give the free LTspice from (then still) Linear Technology a run, liked it and switched over.
Fast-forward to mid-2019: Spectrum Software's MicroCap (uC) simulator is now distributed free of charge! Accordoing to online sources this would be the best circuit- simulator ever, so I will give that a try soon. I do see a potential disavantage to free software, that it will no longer be kept up-to-date. But we'll see.
Anyway, here is the first resource for uC, courtesy Edmond Verrijn-Stuart: http://www.spectrum-soft.com/usernotes.shtm