Depends on who's doing [or paying for] the feasibility study!
It could well be argued that as this is a TfW service, with TfW stock, it should prioritise the Welsh stations.
Taking that starting point, it's easy enough to argue:
1. Upton doesn't need a train service, it has a bus every 10 mins to/from Liverpool that passes the station.
2. Whilst Heswall [Hills] (the clue is in its former name - it's actually nowhere near the centre of Heswall, which already has a frequent - if rather slow - bus service to Birkenhead and Liverpool) ... could do with better than its present hourly bus service, that's easily rectified - just double the frequency (i.e. add another Solo to the mix) and tweak the route to connect with Merseyrail at Bebington, Port Sunlight or Spital. Then you'd have a half hourly service to/from Heswall centre, connecting with Merseyrail's ultra frequent services somewhere on the Liverpool - Chester/Ellesmere Port corridor.
3. Neston doesn't need the train at all - the good folks of this ex Mining village have a half hourly bus service to/from Liverpool and an hourly one to/from Chester and the Wirral Coast.
They're TfW units, and Cardiff should therefore prioritise stations in Wales - i.e. all the other ones. By omitting the aforementioned English shacks, the end to end time of an hour becomes easy.
However, I suspect Merseytravel, the Wrexham-Bidston Rail Users Association, and many members of this forum might have a rather different view.