Tried a couple of new buses last month, so capsule reviews:

Transtar First Class, about S$49 one way (-10% with Worldcard). Singapore departures from their "First Class Lounge", walking distance from Lavender MRT. Lounge has wifi, drinks and rather comical boarding announcements by the lounge attendants. This is an excellent way to go: it's a double-decker bus with only about 16 seats, all singles, excellent seat pitch, video/music on demand system, plus edible lunch and drinks on board. There's even a "lounge" downstairs! Some buses even have a Wifi system (in Malaysia only); it was quite spotty, but hey, it's free so you can't really complain, and good enough for sending/receiving your mails. One downside: arrives at the Pasar Rakyat terminal, a bit of a hike from Bukit Bintang.

Nice++, about RM90 one way. Convenient departures from KL's old railway station, passing via KL Sentral so you can board there too, and frequent departures (22x/day!). In every other respect, though, Transtar kicks their ...: half the seats are paired (2-1), seat pitch or recline isn't as good, the video system is a joke (not on demand and only 3 movies), the food is a pathetic little snack box.

The KL-Singapore air sector is heating up more and more though, Air Asia is adding flights all the time and Firefly is about to start flights from Changi to Subang (the old terminal, much closer to the city than KLIA), so I think I'll be opting for the plane next time...