I'd agree these aren't ideally located hotels if you intend to spend most of your time prowling the RLD, but I like staying a bit further out to get a decent hotel at a cheaper price, exploring different areas of the city and so on. There's something nice about gazing out over the city lights (or more often the lights of the ring road and some office blocks) from high up in a nice hotel room.
By coincidence I've just booked my next trip in the "Best Western Premier Hotel Couture". I'm guessing it must be fairly new (?). It's right down beyond the end of the Vondelpark, maybe 10/15 mins walk from Lelylaan station, or next to tram line 2. Looks funky from the photos. I quite like this area (I've stayed in the Westcord Fashion Hotel there), in good weather you can walk right through the Vondelpark into town, or take the tram into the centrum, or just walk to Lelylaan and hop on a train if you want to get to the RLD in a hurry.
I've stayed in the Blue Tower loads of times, it can be very cheap at certain times of the year. It was built in 2006, the rooms are all decently-sized, pretty much what you would expect for a 4* hotel. Can feel a bit cold in winter or hot in summer, air-con takes a while to do its thing. Depending what floor you are on there are some nice views (scroll down towards the bottom of
this thread for some views of the city seen from the Blue Tower). Transport links are good (bus 21 to CS, tram 14 to Dam or tram 7 to Leidseplein) but it's a fair distance from the centre (out west, next to the ring road). You can walk to Dam Square in about 45 minutes if you fancy a stroll on a nice day, but really you will be needing the tram or bus which are fairly frequent. There's a useful large Albert Heijn by this hotel for stocking up on beer and snacks. I like the neighbourhood feel of this area, there are plenty of shops and places to eat but no real night life as such.
The Blue Square is even further out, several tram stops beyond the Blue Tower. I've never really fancied it. I think it used to belong to a different chain originally and the reviews were not great from what I remember. Judging from the photos on Hotels.com it might have been refurbished since then, so maybe it's better now, I don't think it used to be 4*.
The Apollo Museumhotel is actually on the edge of what I would call the centre, between the Rijksmuseum and the Casino. So it would be very convenient for Leidseplein / Museums but a fair walk (or a busy tram ride) to the RLD. I think this is another hotel that got taken over by Best Western, on the photos it looks like the rooms have been redecorated. The room sizes sound very small, they are advertised as 14 square meters for a classic room or 17 for a deluxe. It's a 3* hotel and never looks quite cheap enough, nice enough or central enough to tempt me to try it.
The Delphi would be on tram route 5 or 24, OK for getting into the city, within walking distance of Museumplein but quite a distance from the RLD. Looks quite nice from the pictures....if it was cheap enough.
So I'd recommend the Blue Tower, I'm trying the Couture, I'd consider the Delphi but I don't really fancy the other 2.