Local Vs Remote agency
The first question you want to ask yourself is: where do you want your agency to be? In most cases it will be close to your office so that you can have face to face meetings reasonably often, save on travel costs and have some kind of flexibility. I used to work with an agency just one block away and it was really handy when we needed to drop some products for a photo shoot or go there to clarify some points on ongoing projects.
A completely different option might be to choose an agency anywhere in the world and work with them virtually on the phone, skype, email, etc.. This is a very realistic approach and is made very easy with today's technologies. You might want to choose this option if you live in a very small town with little resources around, if you're very picky and want to choose the best designers on the planet, or if you want to work on a very low cost budget from an Asian agency. I worked with an agency in China on the development of a new website and we were so happy with the result that we asked them to design our product catalogue. We communicated mainly by email and skype chat with the odd phone call, and with a little bit of organisation it ended up working quite well.
Web design agency Vs Marcomms agency
There are plenty of agencies out there and it might be quite confusing at times to know which do what exactly. Some agencies focus only on website design while others offer a broad range of services by leveraging partners' expertise. Depending on your experience with agencies and the level of existing material you already have for your business, you might have different needs.
For example, if you are starting a new business, it might pay to go to a more general agency that will be able to offer advice on branding, messages and other communications activities to tie with your website. If on the contrary you already have a corporate identity well defined, have a set of brochures, and just need a website with reasonably complex functions, you might prefer working with a specialised web agency. They will have more coders and designers in-house and more relevant experience.