How confident are your parents with foreign travel?
If you book a package deal, there should be a rep at the airport who will have transport waiting ready to take them direct to the hotel.
If you use the d-i-y approach, they'll probably have to work out where the bus departs to take them to the city centre. Once in the city centre, they'll then have to find a taxi to take them to their hotel.
In most cases, I'd recommend the 'd-i-y' method, basically on the grounds of cost. If you're sure you're parents won't mind the extra hassle of sorting out transport from the airport to the hotel, you can save a great deal of money by putting your own package together. However, if they're not confident travellers, you might be better to buy an 'off the peg' package. (I hope that I don't sound 'ageist' here. I know that many older people - including myself! - are perfectly confident finding their way around foreign cities. I'm simply accepting that some people - young and old alike - get worried when faced with unfamiliar transport systems).
If you want some suggestions for the d-i-y method, tell us roughly where your parents live (so we can find flights from appropriate airports) and we'll come up with lots of suggestions. (My first thought is Barcelona - which is wonderful at any time of the year - but there's little point in me costing it from, say, Stansted if your parents live near to, say, Aberdeen!).
If you decide that a package deal is better, you might want to visit a local travel agency before you start hunting around the web. They often have 'early spring' city breaks, in February, at prices just as good, if not better, than anything on the web.
Chris