DON- 20BI downswing chances are equal to the chances that your pizza delivery boy is Phil Ivey;
SNG- 20BI downswing is a common occurence, nothing special about it. 50BI+ downswing will hit you if you play enough.
DON- easy to play a trillion at the same time (multitable),
SNG- harder to do, +you must focus a lot on tables with 4 players or less
DON- rather small ROI, i don't instant-believe anyone saying his ROI is bigger then 10%
SNG- easy to completely crush at the micros and small stakes, 20%+ ROI is doable.
Strategy is somewhat similar, but i personally don't like DON's because they limit my agression later in the game (what do you mean i can't push AK into the chip leader for 5BB or fold KK to an all in? - i hate situations like these).
"u don't need much of a skill in those"
False. Do you concieve any situation where you fold let's say KK from BB when a player in the SB put you all in for your whole stack of 3BB and you are sure he is pushing any 2?
And i think they tend to be more filled with regulars because of lower variance.
One little detail remained: MONEY MANAGEMENT IS ESSENTIAL!!! DON't jump it! Ever!