Walking down the aisle

I think it would be nice to ask them both to walk you down the aisle. As you do have a relationship with your dad, he may be a little hurt if you don't want him, but it would be a lovely gesture to include your mum too - I know plenty of people who have done this and had one parent on either side

As long as both your parents are happy with it, then I think it's fine. People who know you will know you have a good relationship with your dad and people who don't, don't matter.

If you wanted to emphasise that you are close to both your parents, you could always get your father to do a reading or to be one of your witnesses. Plus, of course, there are the speeches, if you are having them.

I'd originally thought I wouldn't bother and I'd go on my own, even though I'm very close to my parents. Then my mum pointed out my dad would like it if he could walk me down the aisle, so I agreed but am now thinking I'm close to both, it should be both - it's a more modern way of doing it too, I think.
In your case, I think both is a better option all around, as you really don't know if your dad would be upset, or if he'd say anything (as men often don't), and you've said you have a good relationship with both.