Without doubt the best view is from the layby in Egghill Lane.
Yes, the Frankley Beeches lay-by at Egghill Lane is definitely the most scenic. If you walk south-east from the lay-by along Egghill Lane, there's a field where sheep are often grazed. The view from this location, on a see-for-miles day when the yachts are out on Bartley Reservoir (Sunday?), will net you an urban landscape to rival any in Britain. Take the binoculars and camera!
As others have said, Barr Beacon, and Beacon Hill at the Lickeys, are both excellent places. Also at the Lickeys is Rednal Hill (off Eachway Lane), and not far away from there is [censored] Hill, which offers a 360-degree panorama of south Birmingham. In Yardley, there's a nice view of east Birmingham from Oaklands Recreation Ground, which is off Church Road. Up north (Kingstanding actually!), there's a little-known viewpoint at Clapton Grove, another location offering a 360-degree panorama, this time of north Birmingham.
There was a time when good cityscapes were to be had from some of Brum's multi-storey carparks, but security issues and suicides have taken most of these away from us. If you fancy trying your luck, the best view is probably the one from the roof of Moat Lane Carpark, in the City Centre. Another decent view can be had from the roof of Selfridges Carpark, in the nearby Bull Ring Shopping Centre.