At such an early stage in my training it feels conceited, in the extreme, to bring to mind the panoply of great art and distinguish between art I'd like to emulate and art that I wouldn't. To get within 500 miles of any of these masterpieces would be achievement enough, so why be choosy?
The answer, I suppose, is that "the greater danger for most of us lies not in setting our aim too high and falling short; but in setting our aim too low, and achieving our mark." This was supposedly Michelangelo's view and it really would be conceited to argue with that! Even a beginner needs to know what direction to go in.
So, for what it's worth, here's my attempt at putting it into words.
The works I admire above all are more than simply ingenious. They demonstrate an approach that is decisive and direct, rather than being laborious or mannered. I am also not interested in works that simply aim to shock - that shout too loudly for your attention, but rather ones which speak softly, engage and grow on you and win your love.
I also dislike subject matter that is maudlin, sappy, overemotional or heavily self-concerned. I prefer work that is outward-looking, intelligent and fresh - that takes the viewer seriously and respects their capacity to make an intellectual as well as an aesthetic effort. Separately, I feel paintings should tell us something about ourselves and the world and are more effective when they are articulated with the past. Great paintings encourage fascination and wonder and, like good writing, have a subtlety - tending to "show" rather than "tell" their story.
From a stylistic perspective, paintings with confident brushwork and a unified but refined effect captivate and move me the most. It is here, I feel, that one sees the rare combination of technical virtuosity which still manages to remain lively, sensuous and tactile. This, I think, has something to do with economy of effort - a sort of studied carelessness (sprezzatura). John Collier in A Manual of Oil Painting made a similar point, but 'packaged' for the art student: "There is too much to learn in painting for any man to allow himself to dawdle over it - so he should never do in ten minutes what he can do equally well in five. Of course it must also be recollected that he should never do in five minutes what he can do better in ten".
So, how do you get there? I honestly don't have the faintest idea - but at least it's a direction. I guess the prerequisites are to be self-critical, diligent, energetic and humble - and not to cling desperately to comfortable formulae. With the aim in mind maybe the journey won't involve too much wasted effort trudging down the wrong tracks.