I thought Welsh D's but mine does some bloody stupid things, like when she's in the stable in the day she just has a strap accross the door and when you go in to change her rugs she bites the strap to try and open it.......if I open it for her and she leave the stable door wide open while doing her rugs she doesn't go anywhere!
One of my fave things she does is if you let her in the stable with the bed up she goes to the back to claw it all down!
my new forest i had years ago was very clever- he could limbo under the wooden bar that was used as a gate for the field! his smaller friend couldn't, but he always tried it when he saw me getting his hay net ready for the night! a second lower bar stopped him for a while until he learned to knock that down then limbo under the top one.
I have to disagree on the small front. I have the worlds thickest pony on loan as a companion and he is a Shetland. I honestly have never come across such a thick beastie in all my life. But however it makes him very sweet (unusual for a Shetland I know), I do find his thickness very frustrating at times.
I think that any native breed crossed with a TB tends to be very intelligent. I have had a con x TB a highland x TB and both were/are very clever. Too bloody clever/sharp for my good sometimes.