I've been trying all three lounges over the last four or five months (flying on different airlines, not only SQ).
a) SQ Esplanade Lounge: Nice food and drinks. Relatively quiet. No showers (?). Poor internet (wifi very slow, most pc's provided are broke).
b) Pura Indah Lounge: In my view nicest food and drinks, but tends to be crowded. Too much furniture/cluttered. Showers on request - but nice facilities. Good wifi.
c) Premier Lounge: Nice food and drinks. Can be crowded as well, but less than Pura Inda. Showers on request - o.k. Best wifi of all three (ultra fast).
If you have the choice, it really depends what you want (food, shower, internet, quite athmosphere)?