Gravity takes time to work eventually you may get more out but that will be after a long time, plus remember when you are going to oil change shop your car is still very warm, its not like its been sitting for a day that all oil will be contained in the pan, so suction using compressed air has a better chance of getting more out in a reasonable time period. particles are contained within the body of oil , the ones on the bottom of the pan are only in the case when person has abused the oil change interval or not using a good synthethic oil, and anyway in any case a little oil remaining does not cause any issue unless you are really abusing your oil change times and using non synthetic. ill worry more about over tightening or not using new copper washers which may reduce longevity or possibly cause a leak at a inconvenient time or even damaging the fragile looking bolts of the shields as is common by how much physical force i have seen them use.
do a experiment yourself next time, note the quantity of oil sucked in once change, next time drain using the bolt and collect the used oil and measure it youll have a answer. i do top up changes on my Mercedes and Altis and get more out using sucking, i once got less out on a Pajero mini so it also depend on the engine and dipstick design. though apart from Mercedes in both you still have to go down for oil filter change.
you have both views you can decide whichever method suits you best, further technical discussion will probably not appropriate for this particular thread 
