I would think a small firm will give you broader experience and a large firm will give you more in-depth experience.

Don Phillips
http://worthingtonengineering.com

Think about what you need in your repertoire of experience.

Do your homework online and check out prospective firms that are hiring.  

After you submit your resume, when you are called in for the first interview, interview the interviewer(s) and see if that firm can provide what you need.  See what they do...  Be willing to accept a lower salary to get the experience if you are short in a particular expertise, PT slab design, for example.  

If it is high rise experience, more than likely, you will have to go to a large to medium size firm.  Only you can decide what you need.  Do you have your PE?  Civil?  Structural?

Mike McCann
McCann Engineering

As an owner of a small firm I can say that you would get gain a broad experience if you worked here. We do everything here: storm, water, sewer, sewage treatment, roads, site development, client development, erosion control, secretarial work and janitor work. So small by far.....but then again ive never worked at a large one.

There is no clear cut answer. I have gotten great experiences at both large and small firms. It depends on the people that you interact with - not the size of the firm.

People often say that you get a more generalised experience at a small firm. I often find that small firms do the same thing over and over again - because they are small and are usually limited in their expertise.

People often say that you get pigeon holed in a large firm. I often find that if you ask, you can usually get transferred to another department, project etc. that suits your fancy. People who get pigeon holed I find usually don't try hard enough to get moved.

"Do not worry about your problems with mathematics, I assure you mine are far greater."   
Albert Einstein
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DonPhillips hit the nail on the head regarding the design work.

But I would think that you are focusing too much on design skills.

If you are to go out on your own you will also need to master the softer skills such as marketing, budgeting, client management and quoting. I would recommend that you go for a role that stretches you both technically and responsibility wise.

No matter how much experience you have in these things, you could always have more.

Yes, I have my P.E. in Civil with almost 11 years experience in water, wastewater and stormwater design.  I have worked at firms much like Surcharged's firm.  I feel like I have had a lot of good design experience along with a little marketing.  I was thinking that maybe at a large firm I would have the opportunity to work on larger projects and possibly work with and make contacts with more sophisticated clients.  Surcharged, when in your career did you go out on your own? How many clients or how much work did you have lined up when you went out on your own? What type of clients do you work for?  

Are you looking to expand your engineering skills or your business skills?

Working for a (very) small company will give you a far better idea of what you are letting yourself in for and possible help you hone the skills you will need for when you go it alone. I would recommend you work for a very small company some time between now and then, assuming of course that you have not already.