As for the next-gen Virginia (a current model was just commissioned actually)... It will basically be like an underwater missile carrier, which is an interesting 180 for the US Navy. The design itself will be slightly larger (mostly in length) in order to accommodate a large number of Tomahawk's (as of right now). It will also be less complex and less advanced as well, in an attempt to bring down the cost and raise the rate of production. - Both of which are needed because of budget problems and aging LA class subs respectively. IMHO, it will basically be a cruiser under the sea, but it will also be replacing older SSN's which doesn't make much sense to be honest. It would be like Russia replacing the Kilo with a shrunken down diesel Borei... They have completely different roles... Thankfully (for the US Navy), they should have a decent number of Virginia's (current model) by then. - This newer model wouldn't stand a chance against actual SSN's, and it would also have "cheaper" (worse) sensors as well AFAIK.
The next-gen Ohio replacement is much more predictable... It should have a design influenced by the Ohio, but will be more advanced in just about every way. Interestingly enough, they will only be ordering twelve, and with the Ohio's gone by then, America's SSBN fleet will shrink down dramatically. This is partly thanks to the subs high price, which will be close to three times what the Borei costs if I remember right. Anyway, it should carry sixteen ballistic missiles (same as Borei, down from 24) and will fire the Trident-2 (a life-extension variant). Some have said it will only be able to hold twelve missiles, but I doubt that is anything more than creative thinking.... Besides that, it should use lessons learned from the Ohio and Virginia etc.
The US Navy has no plans to order a SSK AFAIK, because it doesn't fit their strategy and cannot actually be offensive.
To be honest, I don't think that Russia has much to worry about... The US will be reling on smaller numbers (compared to today) of subs, some of which don't really have a role (Virginia-"upgrade"). At the same time, Russia won't be posing a much larger threat to the US Navy because of smaller numbers despite their advanced-nature. So, in all reality, nobody can say this sub is better than this one etc until they actually engage.