If you really want to solo it will be difficult to find the right mob for you. Some mobs are easily killed with lancer while others can be killed with little effort by archer. For pugilists for example it's best to go after skeletons. Other nice mobs are all kind of ahriman(lancer), drakes(gladiator, thaumaturge), raptors(pugilist, lancer, gladiator), salamander(any), basilisks(lancer, gladiator, archer). That's only what I tried to grind solo though. If the mob is 10 ranks or more above you, you get 450 or 600sp which gets less and less with every rank you get closer. Once your rank is higher than the mobs the sp drops dramatically.