I regard to summon spells for pets - I have used them all at one time or another, and I believe the ultimate summon Speel you want on your pet is Skeleton Warrior IV.
I have a soft spot in my heart for Flaming Sword, and it is fine as a start out pet summons, and the pet can use Skeleton Archers surprisingly effectively, since s/he always positions them corrctly.
Blood Skeletons are nice, as they helps keep the pet in-health and in-the-fray. But when you reach the point that you are elegible for Level IV Spells, Skeleton Warriors it the way to go. You pet will pretty much keep one or two active all the time, and despite what you might see in some of the forum discussions, if you keep your pet healthy, with pots or better with fish on Hotkey, the pet will quickly build up to five sword and shield Skellies in a hot fight. That crowd in front of you will allow you to pick your own opponents with a little more care. In my opinion, the shield/blocking and the slightly longer duration and greater hit points/damage on the Level VI Skellies more than makes up for the life-steal/transfer on the Blood Skellies. Also, the pet doesn't seem to keep quite as many Blood Skellies in play.
To keep the pet in health, I also recommend collecting low-level double socket jewelry for the pet. It almost doesn't matter what the enchantments are, but extra strength and resistance are best. You'll be enchanting some extra affixes onto them whenever you don't have other pressing enchantments to do. Then any time you fish up a shimmering fish scale, put it in a pet socket. The +3 HP per turn is not usually worthwhile on your own gear, in competition with other gem benefits, but accumulating 6 of them on your pet means that s/he is recovering at an extra 18 HP / 'second'. (There are actually about 2 game 'seconds', calculation rounds, per actual second, at least on my computer.) That extra recovery rate can keep your pet in fights significantly longer, and help bring them back sooner.
The other thing to do is to keep at least one Hotkey filled with Fish, almost any Fish, but Muckfish, Gloopers, Tunnel Sharks, Pocket Fish, and maybe Bat Fish are best for melee recharges. A Hotkey fish feed when the annoying announcer says your pet is hurt will restore all pet hit points immediately, then it will restore them again in 2 minutes when the fish wears off. Elemental fish are OK, but they are best as the opening transform of an anticipated fight, a 'door-opener', because they are somewhat glass cannons; these other transforms carry some significant extra HP when the pet is transformed. Except the Bat Fish, also rather a glass cannon, but you get so many Bat fish; go ahead and spam them as heal potions, and the Vark form will do some noticeable damabe til it gets hurt. Spiders and birdfish are just too fragile, and bog perch/strider transforms, while packing a good punch (a good scratch?), tend to get in the way a lot.