OnTop is a bit precious - good for instrument failures but a bugger to configure; I found IP Trainer to be better.
RANT is good for spatial awareness and practice.
Never Get Lost by Willhem Tanner is an excellent book that gives an interesting alternative to mental maths. in the cockpit - I found it to be a more intuitive approach to instrument Nav. Do not get the software - IMO it is inferior to RANT.
I have the ASA offerings spare (for a consideration!) as I now have access to aFrasca beastie if you want to buy at a knock down price... if so, PM me.