Which are the best taxi services from Dublin airport to Conrad Hilton?
There's no need to book ahead if that's what you're asking. Just follow the signs from baggage claim and join the queue at the curb.
Your hotel will likely offer some sort of car service if that's your preference.
Regarding your other question re walking tours in Dublin, I'd suggest checking with the concierge at your hotel.
Alternatively, the local TI will offer a number of tours geared to your particular interests. There's probably one within a few minutes of your hotel.
Thank you for your quick response.