D3 is more effective as a preventative measure for cancers,
There are over 20 forms of vitamin D including an inactive and active form of vitamin D3. The D3 sold on the market is the inactive D3 since the active form sells for around $600/kg through raw material suppliers. If the kidneys are functioning properly though then they can convert the inactive D3 in to the active form of D3.
As far as cancer therapies I have yet to find any therapy with the effectiveness and safety of ozone therapy.
Most of the therapies flying around really do not have solid evidence behind them so I advise people to do homework on any therapy they choose from non-sales sites. PubMed is a good start.
I have been working on a book reviewing various alternative cancer therapies to show what therapies really work, which are hype, which have a basis for working and evidence and which are simply outright quackery.