The biggest difference between these is that Steamroller would be your baseline competitive format for use in most tournaments. Hardcore is for an ultra competitive high pressure format with a single scenario. Finally the Masters format is a more streamlined version of the Steamroller format for use at larger venues to determine the best of the best.
So, what does this mean for everyone, lets start with the baseline, Steamroller
The first thing that player will notice is that the number of Artifices in SR2013 is much smaller. While SR2012 brought us Kill Box, Interactive Objective, and Reinforcements SR2013 only has Kill Box as an Artifice. Don't let that fool you though. Reinforcements have been moved to scenario variants and now every objective is interactive and can be damaged. Kill box itself has become harsher and more forgiving at the same time. Unlike last year you don't lose immediately if your Warcaster or Warlock is outside of the box, but now the borders are 14 inches further in, 2 inches more then last year, and if your Warcaster or Warlock is outside of the box you give your opponent 2 control points.
The next subject of note is that Warcasters/Warlocks cannot contest objectives or flags, but they can dominate them if they are uncontested. This means that they score more points for dominating an objective then a unit scores for controlling it. This will make Warcasters/Warlocks who can defend themselves and keep the enemy away all the more valuable in the Steamroller format.
As a note Flags are specifically 40mm and Objectives are specifically 50mm, which just happen to coincide with the Warmachine objectives set
Tournament scoring is the same as last year but now tiebreakers are not done by scenario but are standardized regardless of which scenario is being run.
As far as variants there are a few changes. Character Restrictions and lake of them are now a variant so it may vary from tournament to tournament. Hardcore has its own format which we will cover soon, reinforcements are here instead of artifices, and most interesting is that there is now a Specialists variant. I think that this is the most interesting other then Character restrictions as it allows for a type of sideboard that allows players to prepare for that bad match-up with a Warcaster/Warlock.
A couple things of note are that the killbox artifice can be applied to 5 of the 12 scenarios and 8 of the 12 scenarios have objectives which do something on the battlefield.
A new development for the Hardcore format is that there are awards for Hardcore tournaments. These are:
Vanquisher - Most Tournament Points
Mage Hunter - if you win by assassination, number of models removed or destroyed by you, highest score wins this
Executioner - overall army points destroyed
Master Craftsman - Best painted
Hardcore format has only a single scenario, called Deathmatch. In this scenario there is a single 12"x12" zone in the middle, if both casters live through the game this is used to determine winner. a kill box variant is in effect from 14 inches from board edge that causes magic damage
So, what do you think about these changes to the Steamroller format and about its new child formats? What will this mean for the Warmachine and Hordes tournament scene? you can go here to download the rules and decide for yourself