Personally, I would (if I had to) go for a basic brand that had been around for a long time, without any fancy probiotics or LCPs in it, or which claimed to have a new formulation that did something other formulas didn't.
The statutory requirements don't prevent anything being added to any formula, as long as there is nothing missing, and the manufacturers stick to the statutory recipe. I don't think probiotics, prebiotics, LCPs and nucleotides have been around long enough, frankly, to be sure they don't have long term effects. None of them is from a human source, so just 'cos breastmilk has them, doesn't mean formula is 'better' with them.
I am inherently suspicious of new formulations, like Omneo Comfort, which contains potato starch and whose main ingredient is glucose syrup. Please - how is this in any way 'close' to breastmilk?
But some sort of bog standard infant formula that's been on the market for 20 years or more....any serious side effects of the ingredients, beyond the deficiencies of it not being breastmilk, are likely to have shown up by now.
Babies with a high risk of developing allergies, are, as we have said, a different thing.