I have been using the suction method on my Volvo Penta 2002, Yanmar 3YM20, the wife's VW 1.8 liter Jetta, and several small engines. I know how much oil they should hold and I make sure I remove about the same amount. The suction method won't work on all engines because the suction cannot reach the bottom of the pan, example 1.4 liter VW engine. Draining from the sump probably removes more oil and contaminants, but it makes more mess and generally requires more effort.
BTW my Yanmar does have a drain plug but getting a pan under it and then out without spilling it would be a challenge. I would probably suction out the oil and then drain the last little bit if I really wanted to get it all.