Another vote for Bosch. I just picked up the Bosch 12v barrel grip, and have a 15 year old DeWalt that was the top of their line when I bought it. The blade changing on the Bosch is so much simpler than the DeWalt. I also have a Festool Carvex that I picked up used, but I haven't broken it out yet. The Carvex and DeWalt are both top handle, I haven't used the Bosch (my first barrel grip) enough yet to know whether I prefer top or barrel.
The JS57 series here in the US looks to be the same as the GST 160 series over in the UK, while the JS47 look like the GST 150.
I'm going to use the Bosch primarily for quick cuts (plugging in is a hassle in my shop), and will dedicate the DeWalt to metal work and such, while reserving the Festool everything else.