I have worked for years in both and I think I can offer you a clear insight. Nowadays companies in order to save money avoid building small offices on the same floor and prefer to use open spaces presenting them proudly to clients as a great team work environment. So what's the difference and which one is better?
Closed small office
Advantages: more quiet, you can concentrate easier on your work, you see the same people everyday and get to know them very well, most of the times you have your own desk and own storage places, you have a door you can lock and leave your work safely on the desk for only your team members to see, better information security; you can have a work schedule for the rest of the employees in the company to follow - they can't come in and interrupt you at all times, better time management opportunities, more privacy, especially when dealing with confidential information.
Disadvantages: seeing the same people every day and not getting to know well the rest of the teams in your company can be a disadvantage sometimes since you can't always work with your team members only but need to relate to the other departments; forgetting your key at home can end up in you waiting in the hall way for long minutes until someone comes to unlock the door, spaces can get crowded when there are too many members in your team, too much paperwork or too much furniture; not being always informed about latest news (especially informal ones) unless you go around the company to ask; people in the company don't know you very well and don't trust you for a while at least.
Advantages: you always have a lot of people around that can help and from whom you can seek advice, the atmosphere is merrier; it's indeed a great way to develop the team spirit and build a strong team; you are always up to date with the news; there's always something to learn from the problems solved by the people around you - you always end up learning a solution by chance and realizing you have it when you most need it; it's a great place to celebrate birthdays with so many people singing to you and wishing you a great time; it's a great place to have a Christmas tree for so many people to enjoy it; it's a great place to learn how to share.
Disadvantages: it's always noisy, there's always someone interrupting you from important work when you least expect it, there's never an agreement concerning temperature and fresh air - there will always be someone who wants more heat or less heat or who can't stand the air conditioning; if someone gets sick and comes to work chances are that a lot of the other team members will be affected too; it's very difficult to discuss confidential information or work on a confidential report with people always moving around you; sometimes desks can get crowded, there's never someone responsible to bring paper to the printer and you always have your things missing from your desk (and if you look around they are always on someone else's desk and they forgot to bring them back - it's always annoying to search 80 desks to find your stapler).
If I had to choose now - I would choose the closed office because of the silence, but for all very young people just starting off on their career journey the open space is a great place to work.