The contraindications are: Slow heart rate, 2nd or 3rd degree AV block, sick sinus syndrome, cardiac failure, low blood pressure, severe peripheral arterial disease, lactation, cardiogenic shock, metabolic acidosis, severe asthma or COPD and history of brochospasm.
The risk of developing new onset diabetes in hypertensive patients is 50% more if treated with a betablocker such as atenolol compared to an ACE inhibitor (e.g. enalapril, lisinopril, ramipril etc.) or a calcium channel blocker (e.g. amlodipine, nifedipine etc.) as per a recent study.