It may even be a bit too early to book now, as I noticed that some hotels on third party sites haven't yet released their prices for April yet. But, then again, it never harms to book ahead, if you can grab a great deal!
I would also opt for the YMCA Salisbury hotel, but, you certainly won't be getting the "luxuries" available at the Marco Polo Hotel. For me, price (and location, which, in this case, both are fine) is more important than "luxury", so, I'd certainly go for the Salisbury. Also, it does have largely very positive reviews around here and is recommended a lot, so, I wouldn't have too many concerns, unless, you really want those "extras".
I don't know which dates you're looking at in April, but, take a look at www.asiatravel.com/ for hotels. If you're in HK before the 11th April, prices at Tin's suggestion of the Harbour Grand for a Superior Harbour View room is $1188HKD per night, Deluxe Harbour View Room is $1298HKD per night, and Grand Deluxe is $1463HKD per night. After the 11th, the prices shoot up, unfortunately. The "downside" to the Harbour Grand (mentioned quite often in the TA reviews) is the location, which is more residential than tourist-ey, which some don't like (but, I don't mind at all). However, given that you're only a few minutes walking distance away from the MTR station, you honestly won't have any problems in getting around.
Good luck with your planning and have an AMAZING time in HK! :)