We've got a cheapo plastic table, which has done us proud for the 4 years we've been camping. I'm amazed how long it's lasted, given how flimsy it feels, but I think it's now time to upgrade.
There seems to be 3 different grades of picnic table. There are cheap ones like ours, or this one.
Then there are the mid-range aluminium ones like this: Quest Folding Aluminium table This looks nice, but the reviews are pretty bad, saying the surface degrades in the rain.
I'd go with a cheap one. We've been all around the houses with camping/picnic tables over the years and more expensive ones don't seem to have any significant advantages in my experience.
We have the mid range Quest one and it has done well for about 5 years of abuse by my 2 young boys, left out in the rain, giant pine cones thrown by French squirrels and even blown away in a gale! It seems flimsy but seems to cope. No problems with the surface degrading. It's a bit tatty now but I looked for a replacement and came to the conclusion that it's the most convenient table arrangement for us so will replace when it finally dies! I didn't pay £60 for it though! We paid about £30 when it was on offer, but I probably would buy again at £60 if I couldn't find it cheaper.