Neither. Since it's exam time for me, I haven't been playing my main save at all lately. After the last time I played it, I opened it up in MCEdit and deleted all the chunks that weren't in the immediate vicinity of my base. I hadn't built anywhere other than one spot, so I didn't lose anything, and the only reason there were many chunks to delete was that I went exploring a while back, but didn't really find anything I liked. So when I load my save after the update I'll have all nice new biomes to play around with (hopefully)
I would start new, but found an epic map today that forms an island archipelago of sorts. I am keeping that map as it is (haven't really started yet, only 1 mb atm) I think I am going to make an epic harbor there, the terrain is just too awesome not to. Then I think I am going to keep my 7mb map that is only kind of explored. I have a large land mass and an oceanfront mountain fortress in there still. Deleted my first three games already, and then a few other maps that had interesting terrain that I planned on exploring.