Hi Dave...
That's such an open ended question, you'll never get a definitive answer
All bikes come at different price brackets, dependant on groupset, frame material and wheelset quality.
Any bike within that particular price bracket will be comparable with another...in that same bracket.
Take the major manufactures 'entry level' bikes...Bianchi, Felt, Specialized, Orbea, Giant, GT etc etc etc...they all cost circa £550 to £700(roughly)...and they'll all perform quite similarly.
They'll generally come with Shimano or Campags entry level groupsets (Sora or Xenon), both of which are comparable, and reliable.
Usually, whether you buy a particular brand comes down to personal choice...not because one is better than the other.
Which is the ultimate beginners bike ?..i'd say any of those entry level bikes. Anything cheaper, you sacrifice too much somewhere...and eventually you'll realise it. An example...
My Raleigh chimera, at £250 some years ago, was a
brilliant buy...good strong wheels, Sora groupset, done several thousand miles....excellent value for money, never regretted buying it
but the frame was heavy and you realised it when lugging it about, and especially on the hills.
My Bianchi falls into a higher bracket price wise (the entry level bracket) but the frame is light. Its a delight to ride. It accelerates quicker, deals with hills better, more responsive in traffic, more comfortable etc etc etc.
Then there's the intangible 'joy to own' feeling. I still love it a year later...where i always thought of the raleigh as a workhorse.
For me, any of those entry level bikes in the £550 to £700 bracket will give good service, be a joy to own, fast, reliable if looked after etc etc...any of them are the ultimate beginners bikes.