^Buying Bitcoin with lump sum is the best strategy but the problem is not everyone can afford to dump at once which is why DCAing is very effective for accumulating Bitcoin even for the retailers. And also I wouldn't say selling at high is wrong because that's the basic of making profits by selling an asset while we can't really draw the line which is high and which is low due to the highly volatile nature so all we can do is just go with the instinct and try to make best out of it.
Every strategy in bitcoin investment is good for accumulating bitcoin, and if we must single out the best strategy for accumulating bitcoin, I think that should be the DCA strategy. The reason is that it has proven to be effective in accumulating bitcoin, and it has also helped so many investors who think that it's too late to invest in bitcoin to get started with their bitcoin investment, and they are consistently accumulating bitcoin either on a weekly or monthly basis. Since the lump sum strategy is mainly for rich folks, it can't be ranked as the best strategy for accumulating bitcoin because not all investors can use it to accumulate bitcoin.