Frankly I think EE's long-running roaming plans had always been pretty decent value - and although 3 "like home" has been around longer (well, it was there a few years ago, withdrawn, and reintroduced) EE's roaming plans always had far more "useful" destinations in there. Also, EE had the bonus of unlimited free calls to all destinations within that zone while roaming so if you were in China you had unlimited free calls to USA, India, Australia and so on and not just the UK. EE also includes Switzerland and Norway within the free roaming zone, where other networks often rip you off due to their exemption from EU roaming rate caps. Finally, EE's equivalent of "like home" includes 58 countries, including all of 3's destinations (except maybe Hong Kong)
Vodafone also has lots of Europe in their use-your-allowance-abroad Eurotraveller plan including important non-EU countries too (i.e. Switzerland and Norway)
So 3's proposition isn't really all that unique. It includes the least countries of those lot, the only real difference is it's included for free.