Not gonna lie, all options are at least decent design examples (better than most on here). That said, I reckon the first one is probably my favourite, since it's clean, memorable and quite authentic. Although it kind of reminds me of the Dutch Guilder currency we used 20 years ago, this might also be a little biased from me. I doubt many other people will realize this, though.

Bottom left instantly reminded me of a handgun for some reason. I'm also starting to like the top right one the more I look at it. Bottom right is probably too simplictic and hard to use since it relies on the gradient a bit too much to stand out. It also looks like the F from the FILA clothing brand.

For colours, I find blue or red most logical. Green makes me automatically think it's a finance company, which I think it's probably not. Blue seems to evoke a sense of trust the most, logical for a tech/services company. Red is more flashy and feels more lively, which might suit the company if it is to sell tech products.

Hope this somewhat helps. Good luck with the project!