DO I us the trading date or the settlement date when filling in the date of disposition for capital gains.

Use the settlement date.  For more info, please see http://www.taxtips.ca/personaltax/investing/taxtreatment/tradeandsettlement.htm

TDAmeritrade says you are wrong: Thank you for contacting TD Ameritrade. In regards to your inquiry, ownership of a long position begins when you make the purchase of those shares, therefore, the actual trade date is used in determining the holding period for capital gains and losses.  You may reference IRS publication 550 for additional information.