I'd say my top five favorite Pokemon introduced in Generation 5 would have to be:
Oshawott/Dewott/Samurott - I fell in love with Oshawott from the moment it was revealed mainly because I find otters adorable. I don't mind the fact Samurott becomes quadrupedal, it's a great design and will always be my favorite starter in Unova.
Rufflet/Braviary - What can I say? He starts out as a cute little eaglet and evolves into a powerful bird. My only criticism in BW is how you have to wait till Opelucid City to capture one. At least in B2W2 you can capture one earlier in the desert area.
Deerling/Sawsbuck - I love Sawsbuck because of multiple reasons, artistically it being grass type makes more useful than Stantler. Ascetically the fact it changes appearance every season gives it personality. Winter has to be my favorite form!
Sandile/Krokorok/Krookodile - I fell in love with with this whole family mainly because of how powerful it proved to be in my first playthrough of BW. Krookodile has lots of moves to choose from and can cover lots of weaknesses. The fact Ash caught one in the anime made me fall in love with it even more.
Zekrom - Zekrom was the first legendary Pokemon that I actually felt a strong connection too. It reawakens at the perfect moment and chooses you as it's trainer to help save Unova. Everything about it is perfect, it's sleek black design, it's unique type combination of Electric/Dragon, and the fact in embodies the concept of ideals.
I love this spooky chandelier, it easily makes my top 10 Pokemon of all time. I adore the colour scheme and design (the blue/purple flames and yellow eyes just look great), it has two great abilities and a solid moveset (gets Ghost, Fire, Grass, Psychic and Dark moves, it's awesome) and I even love Litwick and Lampent! Ghost/Fire is a superb typing and I just like using it? Next time I get through Unova I'm adding this thing to my team, may even get an egg for the start of the game because it's only weakness is how late you get it in BW/BW2. Oh and it has a really cool cry.
Not the original Bug/Steel type, but goddamnit do I love Escavalier anyway! It's evolution method is pretty wacky (annoying for sure, but still kind-of cool from a lore standpoint) but the design is superb and it has a solid moveset all things considered. I also love its cry, for what it's worth. Kind of wish it was seen more in the anime (Ash could've used one, maybe giving Cilan Accelgor or something) but still it's one of my favourites.
Eelektross was one of those Pokemon I always had to use whenever I made a Unova team. Not sure why - could be my love of Electric types, how it had no weakness thanks to Levitate, the colour scheme, the wide movepool or the fact that it was just something rare that my friends never had the patience to hunt down and catch. The Tynamo stage always sucked despite grabbing it before the Flying gym, and Eelektrik kind of felt redundant since you probably got the Thunderstone before you found a Tynamo anyway? But still, I love the eel.
- Emboar: very unpopular opinion, but this is my favourite starter Pokémon of all time. The whole evolutionary chain is great looking, characterized by a colour palette which is wonderful in the slightest of the terms.
- Samurott: it has an amazing movepool and I just really like how it becomes quadruped, running into sharp conflict with its previous evolutionary stages. I also enjoy mixed attackers so, yeah, I do love this samurai based sea lion.
- Serperior: this jester-like grassy serpent looks extremely regal and has a more than amazing hidden ability, which makes of it an excellent Pokémon.
- Musharna: one of the very first things I think about whenever "Generation V" or "Unova" are brought to the field. The dreamy attitude surrounding this pink rounded little monster drives me crazy and, surprisingly enough, even its stats aren't bad at all.
- Conkeldurr: this mountain of muscles looks badass and features a few Rock-type's distinguishing marks I like a lot, such as the colour palette and the stone blocks which indeed consist of its own defining characteristic.
- Krookodile: this black striped crocodile is awesome looking and features a very distinctive body's shape, thanks to which does absolutely not fail to depict with perfection its own unique type combination.
- Chandelure: beautiful chandelier, with darkness' flames heated on it which give the Pokémon itself a kind of gothic mood... It has Flash Fire, one of my all time favorite abilities... Yes, it does have my seal of approval.
- Vanilluxe: there's only one Pokémon who's purely Ice-type and has a three pieced evolutionary chain: this living vanilla ice cream. It could easily be an Ice-type starter Pokémon!
- Volcarona: this moth resembles a star... a star made of fire. The colours by which is surrounded though, particularly speaking of the wings which look a bit like leaves, make me think about the autumnal season for some reason.
- Keldeo: one of the most aesthetically pleasing legendary Pokémon of all time, in my humble opinion. It is super cute and features a nice variety of colours which almost make me think about a rainbow.
Volcarona: In B/W2 you could catch this thing at around 35. It know jack for moves and didn't learn anything decent until the 50s. I remember being stuck with signal beam for the longest time. I also remember this thing absolutely obliterating everything in its way no matter what moves it had. I loved using Volcarona. It quickly rose up to become one of my all time favorites.
Dewott: In the battle of starters the 5th gen starters are the black sheep of the family. Most of them are kinda just eh..... I liked snivy when it was first introduced and used it in my first B/W1 playthrough. I quickly found that it's offensive stats were really really bad and that dropped my opinion of it. I've literally never used tepig before and don't plan on it. So that just leaves Oshawott. The oshawott line was never really my favorite starter line but it was certainly my favorite of gen 5. Dewott in particular is in constant competition as my favorite middle evolution starter alongside Wartortle. Both are for asthetic reasons. For Wartortle, it's cause I really like its tail. For Dewott, I love that it uses its shells like 2 swords. Like just imagining 2 water swords from this thing is just cool.
Reshiram: In the battle between truth and Ideals..... both kinda have their points but I like the way Reshiram looks far more than Zekrom. That graceful white appearance with the blue eyes and the red from its engine tail when it's attacking and you got me hooked. That's all I got really. Aesthetics typically win the day for me.
Reuniclus: It's cute...... no really that's it. It's just really really cute. Like I'd like it's stat line up more if it's speed wasn't absolutely abysmal. I used it a few times in my playthroughs over the years and I can never get over it's stupidly slow speed. But the thing is just so FLIPPIN ADORABLE!
Galvantula: Ironically, I have a fear of arthropods. But the zappy tarantula might have something to say to that. Mainly a compound-eyes thunder to the face. ......I don't think that'll alleviate my fears but it will help me like Galvantula.
Keldeo: Vic mlp is best mlp. No but seriously, I like the hat mane thing it's got going on, it's resolute forme is cool....... also VA. What do you want from me?