[Q] 2014 - is it really "sluggish?" topic

I am interested in upgrading from a 2012 to a 2014 edition.
Can some of you please comment on reviews that say there is "sluggish" performance with the 2014 (I would get a 600 wifi model).

Also - is there a performance difference between the 16GB and 32GB models.
I would use the expansion slot.