A newer Stern will have the most depth but more expensive. ST is my favorite modern Stern and you might be able to find a used pro for decent money. TSPP was also one of my favs and has super deep rules. They do hold their value pretty well so not the cheapest. Shadow is not that expensive, has modes, and a lot more challenging than HS2. Congo and I500 are also great mid 90's games but kinda rare so prices are going up. Just keep finding games to play to see what you like and keep an open mind. Some of my favorite games are ones I thought I would hate or used to not like.