lillipup was in my final/elite four team. stoutland. i'd say it's worth it, if you don't have something that can use a dark type move (crunch) or need a general filler (normal type learns a boatload of special moves, surf, wild charge, among others)
patrat, i didn't use. same with purrloin and audino. audino seems like it's tailored for doubles/triples, but it's basically a chansey. which means you don't really need it for in-game playing, but it's a staple in some teams competitively.. but i dunno if audino is that.
i'd suggest munna/musharna, and a timburr/conkeldurr. they learn calm mind and bulk up, respectively, and can sweep through anything in the game, granted you have a few super/hyper potions to heal them while they set up that. once you have enough stats, just attack and be done. munna learns psychic at 39, but if you want to teach it moves, evolve it whenever you want. conkeldurr is great if you have someone to trade with, if not, sawk (in black) is a great replacement. also, reuniclus is good and could replace musharna, if you're in white. it's a bit slower and doesn't have as much HP as munna.. but it's stronger, and has a better ability for the most part.
a fire type is extremely useful in the middle of the story, but it isn't so much in the last bit. still has it's uses, but it's not as easy as the beginning. fire pig really cleans up. also, darmanitan or whatever the pre-evolution of the fire ape thing is. you find it in the desert, if i'm not mistaken..
andddddddd i think that's about all the tips. if you're stuck somewhere, i can try and help.