Dublin born as I am,I'd agree with Paul,it's either,the merrion or the four seasons.I love both.
My advice would be the merrion though as you can walk to a lot of the general city centre area from there if you are energetic.
I'm talking the square mile around o'connell st including grafton st,up as far as Guinness[at a push] and temple bar.
There are hundreds of quaint and nice restaurants.
Patrick guilbauds is fantastic in the merrion and l'ecrevain is around the corner.
Hugo's is a favourite restaurant haunt of mine nearby on merrion row too.

I find thorntons a tad cold as a restaurant.As a hotel the fitzwilliam is probably better described as a very good four star.Personally I would far prefer a library suite in the westin to the fitzwilliam to be honest.
I wouldn't touch a normal room at the westin with a barge pole because they are ordinary but I love their suites so maybe thats an option for the budget.
I've used the westin a lot as an spg plat.
I know vuittonsofstyle is going to kill me but I find service there to be quite warm and you can't beat the location-a suite only though if you choose there.

I'd agree with Linda,that the fspp rates/amenities would make the four seasons stonking good value.
Their restaurant might not have awards,but as a regular customer,it's lovely!
I also like the bar there [not the ice bar] and the lobby lounge.
As Paul says,it's 10 minutes by taxi into town from there so not an issue.