Kingler, Muk and Palpitoad have never been known to travel with Ash. Every appearance they've had were either at Oak's or when he called for them. While they've all been showed to be powerful, they don't have a massive list of wins for lack of appearances. (Muk's only win was against Bellsprout)
Tauros and Heracross have traveled with Ash, but for very short periods and have also suffered in the way of screen time.
Kingler's latest appearance was just before the battle frontier saga and it had a very small cameo. It's last appearance before that was another small cameo before the Silver conference. The last time it did anything intresting was the whirl cup; even then it was only one episode where it lost to Psyduck in battle.
Muk's last big appearance was the battle with Gary. Since then it has made one small cameo in the Advanced Generation, Diamond and Perl sage and best wishes series each.
Tauros has not appered since the battle tower. However it was shown battling Alakazam and drawing with Metagross
, even getting to train with Ash.
Heracross has not had too bad of a time, it got quite a bit of glorification in the three saga's it has appered in.
Finally Palpitoad dosen't seem too bad either, but unlike Leavanny and the others. Ash has brought Palpitoad to the team for tournements and gym battles and had never traveld with him.
So if either of these five could rejoin the team permanatly like Phanpy did, which would you choose?