Yeah, I suggest the symptom which makes you grow feathers. You get +18 speed, -20% weight and the penalty is you can't wear cloaks.
Apparently it can be even more than 18 speed. What does the -20% weight mean, though? Is it like your character's weight on the character sheet or does it have actual game effects?
Side question: can you get ether disease symptoms that you already had before, but cured? Being a living mana battery was kinda cool, and I think it's the only way you can learn Teleport Other besides wizard dreams and scrolls of wonder.
More than 18 speed? Well, it gives me only 18 speed more but I'd love to skyrocket my speed further if I knew how.
-20% weight applies to your inventory so the total weight of items you carry weigh -20% less.
You can get the same symptoms you cured yourself of before. Still, you don't have a high chance of getting the same symptom considering the number of possible symptoms you can get. My suggestion is, when you get a symptom you want to keep, cure it anyway if you got much worse symptoms before that. If it's your first symptom, just wait until you get two other symptoms and chug a potion of cure corruption (not blessed). You'll be only left with the symptom you wanted to have.
BTW, I'm still playing with the base Elona. I tried Elona+ but then reverted back to the old version after realizing that I liked the original better. Call it nostalgia filter, maybe. Changes aren't really drastic but if you really know how the game works (like the chances of something happening, some tricks that can be done with savescumming, etc) you'll realize that the game changed a lot in the background.