I learnt with Safari (p.d. Carmen) and, as others have said, the facilites may not seem up to much but the instructors/guides all seemed professional and looked after us well. The bonus is that the school is situated RIGHT on the beach front, so walking to the water fully kitted is not too much of a chore.
I have since also dived with DiveCollegeLanzarote
http://www.divecollegelanzarote.com quite a few times and enjoy the diving in and around Playa Blanca. This may be a little far if you don't intend on hiring a car but I would recommend it as an alternative to Carmen if you fancy a change.
Dive safe
Mark