The Giro 2005 was fantastic, just as the edition of 2010. They both had everything, but in 2010 you had a two-dimensional fight. First you had the fight between the big and natural GC man (Basso, Nibs, Scarponi, Evans) which was really good. But the fact that due to a break, Arroyo and Sastre got 10 minutes, did make it even better.
In the mountain stages, you had the excitement of Basso desperatly trying to drop Evans and Scarpa (which he succeded on Zoncolan), but during these battles, you constantly have to remind yourself on the fact: 'Hey, wait a minute, Arroyo is in pink!'. Where is he? How many time will he lose? Is it enough to still be in pink? So like Basso, you had the pressure to drop your big GC rivals, but also to make up the loss on Arroyo.
Combine this tension to the ''sterrato'' stage, the best stage in the last 10 years for sure, and the crazy first couple of days on Dutch ground, and some classical good breakaway stages (L'Aquila, Peio Terme, Cesenatico), i think the 2010 edition is a little bit better than 2005.
Edit: Now i will think about which year was the best overall