Having owned rifles in the original A Bolt, and now a X Bolt, I have to admit that I like the Browning rifles.
While many did not like the fact that the A Bolt's magazine clipped to the floor plate, I didn't mind it. What I did like about it was that extra cartridges could be added to the magazine without removing the magazine from the rifle, as must be done with the X Bolt.
My 280 Rem was an accurate rifle and would put 5 handloaded rounds into an inch at 200 yards (162 gr Hdy SP over max charge of IMR4350). The 25 WSSM wasn't as accurate, but would give MOA performance with its preferred load, and had feeding issues from time to time.
My X Bolt is the LH All Weather that has been rebarreled to the 6.5 Creedmoor after announcing that they would not build that configuration in that chambering. It is accurate (sub-MOA) with the factory loads that I have tried to date, and will shoot 3" groups at 400 yards when I do my part. It also shoots the 123 gr ammo as well as the 143 gr ammo.
Is the X Bolt as robust as the A Bolt? Probably not
Is the fit and finish better than the A Bolt? I think it is. As is the stock configuration. IMO
Do both models have their pros and cons? Yes
As to which is better or best; that is a personal opinion based on each individual's needs and desires. I like them both for their own strengths.
Like any other rifle available on the market today, each has its merits and options to choose from. At least you have the option of finding and choosing older A Bolts when and where you can, if that is your preference.