Free Exchange compares gay and straight parenting:
Currently, most gay or lesbian parents had their child in a prior heterosexual relationship. As society becomes more tolerant and gay marriage more popular, children born to or adopted by gay couples will become more common. This suggests the typical gay and lesbian couple might be better parents then the average hetero couple. The typical hetero couple may or may not have planned for a child, while a gay couple probably did.
What makes a good parent is tough to quantify. but the evidence does suggest that being financially and emotionally stable probably matters more than gender.