For MW, my first choice would be the CCrane Radio 2E... IMHO by far the best portable for AM broadcast band DXing.
It has a large ferrite antenna and also provision for an external antenna. This is my go to radio for AM BCB DX.
If cost is an issue, almost as good and for less money is the CCrane Radio EP. Analog slide rule dial tuning may be a drawback
for some but probably the best AM radio for the money you are going to find. Best audio in a portable would likely be
one of the GE Superadios if you can find a nice used one (no longer in production).
For LW, in my experience, no portable on its own is going to perform very well. You most definitely need an external antenna.
Problem is that most portables have no provision for an external LW/MW antenna connection. You have to come up with some way to
inductively couple the external antenna to the radio. An exception is the Satellit 750 (reintroduced as the Eton Elite 750), it has an
external antenna jack (on the rotatable ferrite bar) for a MW/LW antenna.
It is a large radio for a portable so that may be a problem if you are into the ultralight DXing thing, but a portable LW
radio loses a lot of its portability because it needs to be connected to an external antenna. An external antenna for LW can be a
rather large affair... Beverage on ground (the antenna, not spilled soda pop), KAZ, flag, K9AY, etc. A more compact alternative
would be a loop or FSL. Whatever, an external antenna is a must.