I haven't had any problems with a 1:1 substitution.  According to the
Crisco website:

It’s always best to use a shortening if your baking recipe calls for
it. Shortening makes baked goods fluffier and flakier, while oils
provide a denser and heavier texture. We don’t recommend using oil to
grease baking pans. Instead, try Crisco Spray and follow with a light
dusting of flour.

So substituting oil shouldn't make the cookies too runny -- maybe a
little more dense and heavy.

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Butter can be used, but be aware that it contains a little water & could make 
your recipe a tiny bit wetter.  However, in my experience I've never 
seen substituting butter for shortening adversely effect the outcome of any recipe 
I've tried it in.  I often use Sprectrum Organic Shortening which is made from 
palm oil, lots better for your body than refined & hydrogenated vegetable oils 
(which will contain tons of transfats).  Some people use coconut oil for the 
same healthy reason, but I don't think coconut oil makes a very good substitute 
for regular shortening because it's texture is too different.  
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We don't use Crisco at all at home. But the texture of things will change 
because Crisco is a hard fat. Pie crusts made with 0 Transfat margarine will not 
have the crunch.

For the most part, you can use butter or margarine instead of shortening, but 
both butter and margarine have water and Crisco doesn't.

There is now exact substitute for Crisco, and if the recipe turns out not the 
same, I ignore the difference and recognize I am eating healthier than the 
recipe author.