Okay, so I've been using these with the velour pads for the past couple of days and they definitely sound different, but it's a very subtle difference to my ears. What I do (think) I hear, is that, as already mentioned by others, they get slightly brighter and perhaps a little more airy, but not so much as to be a major difference (to me that is).
The velour pads are more comfortable for sure, but the pleather is not uncomfortable at all - the velour just give them that extra bit of comfort.
As I mentioned earlier, they definitely leak more sound with velour pads; it's not a very large amount unless you like the volume somewhat high. For usage around the house, I would probably go with velour while sticking to pleather when portable.