Currently in Lembongan since a week, I have dived with both World Diving and Two Fish, I can testify both are very good, very flexible in order to meet their diving guests wishes. Besides that they're located 50m from each other.
I have stayed in both Pondok Baruna (450k IDR/night B&B AC) and TwoFish bungalows (500k IDR/night B&B AC Wifi) both bungalows are quite comfortable with a pool, nice location in Jungut Batu, near plenty of warungs. There is a stretch of accoms right on northern JB beach which also look fine, all with pools : Mainski, Nusa Indah bungalows, Ketut Bungalows, I believe they're all in the same price range.
I think mid and north JB is the best location to get easy access to the dive centres.
Currently there are lots of mantas, been twice at manta bay with 4 and 5 mantas around for 50 minutes. I had the cahance to buddy with Helen from Aquatic alliance (
www.aquaticalliance.org) specialized in manta ray conservation in Lembongan. I know now to differentiate a male from a female
From what I understand they are not seasonal.
The site is very easy and even though there are lots of people (divers, snorkelers) the mantas are not scared at all which makes good opportunities for close photos.
I have to say I have been impressed with Lembongan dive sites, they deserve more than just the usual manta or mola mola hunt. The coral coverage in SD or ToyaPakeh is simply amazing and CRystal Bay is more than a big fish dive, the wall and the bommies are beautiful for wide angle photo.
Still unlucky with mola mola so far but we spotted a thresher shark this morning at crystal bay, coming quite close not more than 15m away... apparently it is a quite rare encounter.
Tulamben : I recommand with no hesitation Liberty Dive Centre. They give nitrox for free and I always ask for private guiding which I get everytime. Their guides know every fish around by their first name...