@tranthidung is right if we based on the previous years which April is the best positive price for Bitcoin.
I don't mean so. It is one of the best, not the best.
Additionally, if I want to find best months, I would like to exclude extreme outliers in early years (2009 - 2013, perhaps) and take a look at means and standard deviations of the rest years till 2021. In early years, price was affected by many factors that now become very minor news for the market.
But what I also think what if Bitcoin is already in advance, what supposed to happen for the month of April was already happened last month (March), we saw a positive 30% and this April could be something a price correction, just my 2 cents.
% of price change for one month depends on open and close prices in that month. Your opinion can be true if serious corrections in March (end days of Marches) have long lasting effects till first day of Aprils. Your opinion will be wrong if corrections happen in middle of Marches and price already rally well, therefore in first days of Aprils, price is not at bottom.
As I said, it is a raw view for the market, but for personal balance sheet, it depends on your entry/ exit prices and when you open/ finish your position.
Here is the updated list of prices per month.
Thanks. In fact, that image I posted is taken from @Lucius. I discussed about it long time ago but don't remember where I did it.