Is it better to invest in Bitcoin now or wait until the May is halving in 2020?  

After the two previous Halvings in 2012 and 2016, Bitcoin has entered a strong bull market which has driven its price up sharply.

It should be the same this year.

The price of Bitcoin will probably not increase directly the day after Halving and it may take a few weeks.

However, by the time the price starts to take off, it will be too late to buy Bitcoin at a price as affordable as it is today.