Of those two,
I'd be inclined to opt for Saxo Markets.
Purely in personal experience over time, have seen and read more moaning about IG than Saxo.
But as demo accounts won't cost you, then it's a matter of which platform you find easier to use.
When it comes to costs for the real thing, then there's little to choose between them..
£8= /trade + ~£8= / month in custody fees. -cheaper as you trade more [10+] over time.
But beware of extra hidden charges in the small print, especially at IG.
Reasoning- IG's so-called 'transparent' fee structure is at the least, complex and overpriced, and at worst, baffling.
& tends to change with the wind, market conditions and every little whim.
Inactivity will cost you dearly !
Just my ha'penny worth of opinion.