an adjustable elbow is smaller AND lighter than a gummed-up spark arrester. And more efficient and labor-saving. And no holes needed in your roof tarp. Need I go on?...
Going out the front or side lets you get to your spark arrestor easier if it does get gummed up as well.
I am very particular about the wood I put in the stove and as you can see I am not burning railroad ties.
Never had a gummed up arrestor in several seasons, but did wire brush it once after spiders decided to make a fly trap out of it while in storage.