I would tend towards link exchanges if I had to make a choice, but would certainly be looking to reinforce the link campaign with a much stronger portfolio of links.
Article submissions aren't all that useful - no point in having content duplicated dozens of times - you really think search engines are going to "value" such pages (and the links on them)? Same goes for press releases.
They have some value if someone picks up on the article / PR and talks about it elsewhere, but other than that...
They both have some value when included within a larger linking scheme. If I had to pick one, I would probably go with relevant reciprocal links. If you're on a low budget, do both. Mix it up with directory submissions too. My 2 cents.