You obviously mean the best source for profit investing bitcoin rather than buying etc...? I wouldn't include HYIP's or Revshare as these project are non-sustainable, Gambling also isn't an investment.
My pick would be trading BTC to USD and buying/selling Altcoins which can be very profitable.
why buy etc when there is bitcoin? and also HYIP's and some other shits that making some scam like pyramiding and ponzi scheme with the use of bitcoin is a bullshit. They are just making the image of bitcoin bad so for all the people who uses bitcoin as a scam, go and leave us who believe in bitcoin and dont ever go back again.