LONDON, Oct 1 (Reuters) - Euro zone stocks were the top investment in the third quarter, clocking up their best three-month gains since 2009 as investors bet on a cyclical upturn in the region.

The dollar struggled the most after a set of mixed economic data raised concerns that the U.S. economy may not be strong enough to allow the Federal Reserve to slow its bond-buying programme.

Europe's STOXX index has risen nearly 16 percent since July 1 on a dollar basis, nearly double the gains made by Tokyo and Shanghai shares.

The STOXX index has gained nearly 9 percent in euro terms, its biggest quarterly gain in four years.

Emerging stocks staged a strong recovery after a second-quarter sell-off triggered by the Fed's suggestion that it would slow the pace of money printing.

The MSCI emerging equity index slightly outperformed developed counterparts with a gain of 7.1 percent.

Benchmark 10-year U.S. Treasuries were in negative territory as investors shifted assets away from low-yielding government bonds into equities.

The dollar index fell 3.3 percent.

The following graphics show the performance of a variety of assets.

Global Q3 asset performance:

Emerging markets:

Frontier markets:

Equity performance by region:

Equity performance by sectors: