get whichever one feels better in your hand. or whichever one you can get a better deal on. or whichever one you think looks cooler. or flip a coin. they're both good guns, you can't make a wrong decision here.
i personally like xd's more than glocks due to the ergonomics and trigger, but that's my own opinion, and relatively worthless. both are reliable and durable, and i'd trust my life to either without hesitation.
i guess the one real consideration here is that you can buy any glock part you want over the internet, and you can't with the xd's, you pretty much have to send it back to springfield to have parts replaced if something breaks.