The Titular, Blonde Heroine
BTVS: Buffy Summers
Pros: Kung-fu grip, upstanding moral character.
Cons: More street-smart than book smart, over-protective of her friends
VM: Veronica Mars
Pros: Whip-smart any way you slice it, keen eye for justice
Cons: Disregards rights to privacy, over-exploitative of her friends
Similarities: Both share pretty, pretty hair, official outcast status at school, teeny-tiny bodies, and hot boyfriends.
Differences: In the brain game, Veronica's miles ahead, but can she drop-kick a fire-demon?
The Goofy Boy Who Happens to be a Friend, but Is Only a Friend
BTVS: Xander Harris
Pros: Everyboy charm, good-natured humour
Cons: The weakest link in the Scooby chain
VM: Wallace Fennel
Pros: Athletically talented, good moral support
Cons: Bit of a push-over.
Similarities: Both represent an average normality that helps their Blonde Titular Heroines keep things in perspective. Also, both lack the ability to disobey the imperious commands of their Heroines, and frequently find themselves in need of rescuing by their Heroines.
Differences: Wallace has a shy, put-upon side, but he has a healthier style and social life. Xander plays the loser card a little too heavily, and depends on Buffy more than anyone else.
The "Good" Boyfriend
Pros: Snappy dresser, snappier un-dresser. Sensitive, loyal.
Cons: Bland, square, whiny.
VM: Duncan Kane
Pros: Ironic sense of humour, good-natured, handsome.
Cons: Erratic behaviour, the occasional black-out.
Similarities: Both Angel and Duncan share a tendancy to be dark, silent, and brooding, with occasional bursts of (possibly) homicidal madness - Angel due to his gypsy curse, Duncan to epilepsy.
Differences: Duncan knows how to crack a smile and a joke without killing himself, and also how to enter into sexual relations without killing somebody else. Angel takes himself a little too seriously, and is actually more entertaining when evil.
The "Bad" Boyfriend
Pros: The leather jacket! The accent!
Cons: The obsessiveness! The rape attempt!
VM: Logan Ecchols
Pros: The heart of gold! The devil-may-care attitude!
Cons: The drinking problem! The crying!
Similarities: Serious mommy issues, predilictions for violence and mayhem with infrequent but highly-anticipated moments of tenderness.
Differences: Spike's more reliable, and more authentically bad-ass. Logan's a loaded gun, and years of his father's abuse hasn't made him any more stable. Spike's pain is endearing, Logan's is a little pathetic.
BTVS: Rupert Giles
Pros: Used to be a bad-ass black-magic punk, now is a warm father-figure
Cons: His change from bad-ass to librarian left him with a terminal case of Uptight-a-litis and Fuddy-Duddy-ness.
VM: Keith Mars
Pros: World's coolest dad, efficient private detective
Cons: Prone to obliviousness, especially regarding The Bigger Picture, and his Family
Similarities: Both provide moments of warm fuzziness when Titular Blonde Heroines need it most, both are willing to go completely apeshit-Rambo-violent when the situation calls for it.
Differences: Keith is the more blue-collar, down to earth, with intelligence gleaned from experience. Giles is more refined, book-smart, and seriously out of date.
The Quirky, Attractive Geek
BTVS: Willow Rosenberg
Pros: Cheerful, bubbly even. Oh, and smart, did I mention smart?
Cons: Shy, quiet, unbalanced.
VM: Cindy "Mac" Mackenzie
Pros: Fiesty, organized, a problem solver
Cons: Morally challenged.
Similarities: Both are talented hackers, aiding our Titular Blonde Heroines with the help of records and databases meant to be kept secret.
Differences: Mac's more confident in her personality, and not afraid to add a personal touch to her appearance. She is also not above profiting from chaos. Willow tends to hide in cutesy sweaters and knit caps until she inevitably snaps, sending her over the edge.
Advantage: Willow - but only because she gets more screentime.
The Bad-Ass Sidekick
Pros: Can kick butt in tight leather pants, knows how to party.
Cons: She's an evil, murderous bitch, and also kind of a slut.
VM: Eli "Weevil" Navarro
Pros: Pays his debts, strong family loyalty, and awww, he cried at Lily's memorial service!
Cons: Dude, you cried at Lily's memorial service, you sissy!
Similarities: Both are from troubled family backgrounds, live on the wrong side of the tracks, are emotionally vulnerable, and look good in leather.
Differences: Other than the fact that they have different parts in their swimsuit areas, Weevil, at least, has his sweet ol' grandmother to take care of, that and the fact that he doesn't kill people just to watch them die. Both live in shades of grey, but Weevil's more good than bad, and Faith's more bad than good.
Advantage: Depends on what parts you have in your swimsuit areas.
Cast Advantage: Tie.