For Sale: Shimano Ultegra SL 6600 STI Double 10 Speed new and unused

im not sure about better mate, as ive had dura ace, ultegra and 105's from this range and they all developed some sort of fault on them. the return spring in particualr, do a check online and you will see for yourself. maybe shimano have addressed this issue with the latest offering? Also, the value always drops once the new stuff comes out.

Not always. When 5700 came out 5600 was actually more expensive... There were some issues due to user error mainly (combination of exposed cables, spray from the front wheel and a lack of lubrication). ST-5600/6600/7800 are considered to be the best shifting levers to this day (if used with Shimano inners/outers and maintained properly; not implying that you did not look after yours) and highly regarded with touring/audax crowd.