Newspaper imho. Wet plant material next to the blotters will grow mold even in my climate. Newspaper goes between the blotters and provides a nice cushion. Don't want indents from thicker plants left in my blotters either.
Some have said that newspaper will leave ink on the plants but I've just never had this happen.
Hope this helps.

I use newsprint as an inner layer for just the reasons Rosa mentions (I have a stack of half-used art pads culled from ex-art major friends, and garage sales, so I use blank newsprint for EVERYTHING)

I use tiles for microwave pressing and I have found that unbleached "Doodle Pad" paper that sells for 1.00 or so works the best for me. It's just another alternative. Kathy ~^~O