in all honesty, i think there's a very small population of dogs who are truly good dog park candidates. much, much smaller than the population of dogs who frequent dog parks. dog parks strike me as a kind of weird invention designed more for humans than for dogs.
To me both of those situations are setting the dog up for failure imo.
That said i take my dogs to the dog park (shock and horror I know). It comes down to being smart and knowing your dog AND the park. First I would NEVER bring a toy dog to an unsegregated dog park because even though I wouldn't bring in a dog likely to see a small dog as something to chase and kill, I don't know that other people wouldn't do that. I also wouldn't bring ANY dog to the segregated park during peak hours and especially the big dog side (the big dog side is actually for anyone but the little dog side is ONLY for little dogs). There can be 20-30 dogs on that side and I've been there during high times and every time there is at least one or two fights on that side. The small dog side is usually much less crowded and I have never seen a fight over there. But I take Mia and Summer during off times in the morning when the park is empty or I go with a few friends when the park is empty. Yesterday we were there almost 2 hours and only one dog came the entire time- a pit bull and we simply moved from the open area to the small dog area no problem. I don't think my two really need all the socialization with other dogs (actually neither of my girls are very dog friendly- Summer is a bit afraid and will growl at some other dogs and Mia has ZERO interest in other dogs). But since I don't have a yard having a few acres of fenced off dog park is nice to let the girls stretch their legs. But you have to be smart with it, especially me with Summer. No way would I bring her unless it was empty or mostly empty.
Even going and trying to avoid people I ran into a JRT the other day. The owner kept talking about how the dog would fight other dogs and be hanging off their necks and still she brings it to the park. Needless to say we left pretty fast.