I have two flash's

The first has a Simjet 3000 (30 lbs) Flies well and fast.

The second had a Wren Super Sport, 18.5 lbs thrust. It also flew well and felt much lighter in the air. It did struggle a little bit to get into the air but once on step it was fine. I have since put a Jet Central Cheetah in it (31 lbs) and it flies awsome. Most of the time I fly it 1/2 to 5/8 stick but it has the thrust for great vertical when required.

It is just a metter of preference.....