Skell is a fine DD (can't say much cause mine is 30 lvls behind me...) and I would suggest getting a "tanker" pet as a dual companion for it.
You will buff skell with stability (less threat buff) and Orc/Hawk/Yeti with intimidate (more threat buff) to make sure skell survive.
Using Skell/Sala would be fine too but as both got low vit/pdef, you will ran out of mana (and HP) healing them.
If you want to grind mobs 15~20 lvls higher than you, i suggest a poultry or siren for its unity toggle (Pacc on poultry, Pacc/Macc on siren). The combination of those 2 pets can provide a few dogdes if poultry crow lands on mob and siren's painful noise lands as well (at lvl 10 of both you will have -15% Pacc [poultry crow] and -20%Pacc/Macc [painful noise]).
The pet combination above was tested on veiled island with the BS and pets from my signature, facing wolvies lvl 121~124 (BS and poultry with Cleric and huna buffs, +2 Power Support and +3 Aura of Halisha). Later a blue pixie proved to be more effective than the siren

as she was providing the healing for the 2 DDs (char and pet).
The Pet discussion section on forum gives you a glimpsy of pet skills and builds, do a little research before choosing a pet.