Hey there Ganeshwar! I might be able to lend a hand of advice, although in the end the decision is yours. So let's take a look at what you're considering. For number one, to be quite honest both of them aren't the greatest battlers although if I had to choose the better one out of stats and movesets, honestly I think Ledyba would make a good choice although they're both quite similar asides from typing. Their stats are roughly the same but Ledyba takes the cake for me with it's moveset diversity.
For your second one, Heracross easily. It has a great move coverage and is a fast hitter, that can quickly wreck through teams. I've used a Heracross before and it was one of the greatest decisions I had ever made when playing through a Pokemon game, it can learn moves like Stone Edge and Close Combat, has a unique typing and overall better stats. Although Scyther who later evolves into Scizor isn't a bad choice to consider either, you have to remember if you chose to get it to Scizor, a 4x fire weakness gets thrown in. But overall out of those two that I've just mentioned, they're both badass, you'll just have to consider the pros and cons. Heracross has a 4x weakness to flying while Scizor a 4x to fire. If you hate 4x weaknesses though Pinsir is a good choice although personally for me Heracross is the best in-game wise.
Number three depends on what sort of Pokemon you like. Spearow is more of a speedy and fast hitter and Pidgey is bulky but slower. Hoothoot is rather frail but also rather nimble and can learn moves such as Hypnosis and other moves that both birds can't, but overall I'd suggest better flying types such as Zubat and Natu. They're more diverse and learn a better movepool, but yeah it's all up to you like I said.
Number four, both Pokemon are similar but have a few differences. Nidoran M is more focused on offence while Nidoran F is better in defense, they also learn different moves in their final evolution. The few moves they can learn levelling up is for Nidoqueen things like Superpower and Earth Power while Nidoking can learn powerful moves such as Megahorn. If you like offense then Nidoking is definitely the better choice while for defensive Nidoqueen.
Number five, Oddish any day. Sunkern is weak and frail and can easily be beaten by other grass-types in stats and movepools. It's stats are so awful, it's been classified one of the weakest Pokemon in existence. Also Oddish has a second typing Poison, which can come in handy and add diversity to it's movepool. It can learn Status Condition moves and things like Petal Dance depending if you evolve it into Vileplume/Bellosom. So Oddish all the way!
Number six also depends on a few things. If you like walls but don't mind working with Pokemon that'll almost always get outspeeded, Slowpoke is your choice. Also which type do you like better Psychic or Fighting? Slowpoke also has a second typing Psychic so that can give it all sorts of types of moves while Poliwag has two choices of evolution, Politoed and Poliwrath. Poliwrath is famously known for being a great offensive battler and would make a great addition to your team while Politoed is great in rain teams with moves like Perish Song. But yeah offensive, Poliwag and defensive Slowpoke, it all depends on what sort of Pokemon you like.
And lastly number seven. If you have the ability to trade then Gastly definitely, it's final evolution Gengar can do wonders. It' can easily outspeed most Pokemon and it learns moves out of its typing such as Thunderbolt along with sneaky status condition moves like Hypnosis and the infamous Destiny Bond. Misdreavus however is also pretty diverse but you'll have to wait late in the game to get your hands on a Dusk Stone.
I hope this advice was useful and if you still have any questions, feel free to ask.
