I’d love to get your opinion on these icons. There will be 4 next to each other.
Don’t worry about the context they go into. I’m designing from scratch. I know flat is in fashion but still 
Forgot to add on the image that A2 could be hover for A1 or the other way around.
Thanks.
Well, I’m not very fashionista, and should say:
- If you want the visitors to click on them, they have to be clearly different from other images on the page (the pure illustrations or design things).
- Traditionally a link was an underline text or a UI-button. Visitors are used that clickable items associate to that, and expect that they are more or less buttonlike: 3d.
- A 3d suggestion can be made by a bevel, or a (subtle) border with some shadow: then the visor knows the (important) area where to hover/click. That is is recognizable, user-friendly, and more calling to action!
- Besides a sort of 3d (if the rest is flat), the difference with other images could be also: an introduction text line ("Here you can find our activities: "), the position on the page, a different background color, a different border, a different shape, a different …
Personally, I don’t like “just flat images” too much (with some exceptions for common known logos or icons like Facebook, LinkedIn and so).
But as always: “what is the best, is depending of the rest”, the context of the design of the whole page!