ST, AC/DC and TWD - all great games... so go for all of them, maybe not at once but within the next months/years.
If your budget is at this time "Pro-only" - then I would go for ST Pro. With ST there is from my point of view no need to upgrade to a premium or limited version from a players perspective.
Other than that AC/DC Premium > TWD Premium > ST Pro or Premium
AC/DC and TWD should really be Premiums/LEs. It's obvious for AC/DC and for TWD "only" the walker bombs make the difference.