These little portables are all full of compromises, so I'm not sure any one model is going to be the best all-around for AM and FM DXing.
I'll throw one that's an off-the-wall choice at you: The CountyComm GP-5/SSB. I don't know if it's technically a part of the Tecsun/Kaito/Grundig family or not but it is one of my favorite radios for casual DXing. It's a super tiny handheld radio, and only has a teency little ferrite bar inside, but it comes with an external larger bar that plugs into the AM jack on top and is rotatable for best results. It's still not big — maybe 3.5" inches long? — but this little radio packs a punch despite its diminutive size. I'm also suitably impressed with its FM chops; it pulls in some of the weakest signals that the other radios just miss completely. It rivals my Grundig G8 in that respect, I believe.
The radio does have some significant downsides, however. It lacks a numerical keypad, so there's no direct entry. Tuning methods and the way you select options are best described as "obtuse", and the speaker is exceptionally tinny due to its small size. You can't really quickly jump from one side of the band to the other like you can with more normal portables. There's a pretty big chuff-mute when tuning, too.
It does have a headphone jack, which negates the speaker issue, and you can plug up just about anything to the AM jack and experiment if the included ferrite bar isn't up to snuff (there's a longer version on eBay, 8" I think, from Greece, but it doesn't really help all that much over the stock one.)
The only other portable I use semi-regularly for quick DX sessions is a Kaito KA1103. It's sensitive on AM and FM (moreso on FM) but lacks selectivity, and again QC is an issue. My AM is spot on, but on FM it's off a bit. For example a station on 105.7 is strongest at 105.75. But there's no soft muting, it's super smooth knob tuning AND has a non-standard but perfectly usable keypad for direct entry.
I use the Kaito with a Tecsun loop for AM work and it does great. The CountyComm works the same with or without the loop - also great.
Frankly, for FM, none of them have the selectivity of my little Insignia HD portable.