The main argument I hear from designers in favour of agencies are that there's a lot more variety since you work on a lot of different situations, and that for a less experienced designer there's more opportunities for learning from more senior figures.<p>The main things in favour of working at a company (start-up or otherwise) are more creative control and the opportunity to perfect something as there's one focus for a sustained period of time.<p>A lot of professions have this wide vs deep argument for people at the start of their career. I don't particularly buy that either one is particularly "better" over the long-run - capability floats to the top eventually.<p>I do think culture is key, and particularly how we react and fit into different cultures. I'd have said the size of the agency or start-up is more important - people who come from large companies sometimes find it hard to fit into a small organisations and vice-versa.