5e
So...let's talk about the SCAG cantrips.
http://engl393-dnd5th.wikia.com/wiki/Booming_Bladehttp://engl393-dnd5th.wikia.com/wiki/Green-Flame_BladeMost of the analysis I do is stuff in the core three rulebooks only. PHB, DMG, MM. But there is technically one other book, the Sword Coast Adventure Guide, which contains...two cantrips that people talk about constantly, and I dunno what else. (Is bladesinger Wizard in there? I think it might be. OK, so that's pretty strong too).
I'm not sure what to make of these cantrips. By level 17 if you get full value out of them you're looking at 7d8 damage. This is 31.5 damage. This is similar to sneak attack after 17 levels in Rogue (9d6 = 32.5 damage). You can do both, of course, and have a Rogue hit really hard. But on the other hand, Rogue could use the buff so....
In general, they encourage making single attacks instead of multiple attacks, which I guess is fine since typically the most optimized damage I found was via multiattacking. They encourage melee, which is also fine since hey, Sharpshooter+Crossbow Master is pretty good. They're a pile of damage added on if you hit, so you're not encouraged to use the +10 on great weapon master.
All of this is actually pretty reasonable, and offers a different vector to build characters. Where things get a little strange is that Sorcerers become pretty good at melee. These are cantrips, after all, and that means you can Quicken them, and do them twice in one round. Draconic Sorcerers can also add their Cha to (one of the damage rolls of) Green Flame Blade. I've actually seen someone on a forum ask "why play Paladin when you can just play Sorcerer instead?" An interesting question.
So...making a Sorc front-line build here...I think we want Warcaster (lets us make attacks of opportunity with SCAG cantrips). I think if we're really focusing on melee attacking, we want to dip another class for shields and a better weapon. (Fighter 1 gets shields, and, say, Dueling fighting style).
Options other than Fighter are...Paladin (meh. Like...ok, you could go level 2 for Fighting Style and smites. Except smites aren't that great--if you want to deal more melee damage in a day, you'd do better converting some spell slots to sorcery points so that you can quicken more cantrips). Ranger (meh). Druid (you get a shield, but no weapon). Rogue (you get a weapon, but no shield). Cleric (yeah, this is a solid reasonable option, particularly because it keeps your spellcasting progression going; needs 13 wisdom though. But I think taking Tempest Cleric to level 2 for the maximize channel divinity is a solid option; that build is less about being a melee master, though so I won't focus on it now). Barbarian (you can't use this cantrip while raging).
Once you have Fighter 1, eventually you probably want to grab Fighter 2 for action surge. And once you have fighter 2 on a character that focuses on melee attacking, I think Fighter 3 (Battle Master) is probably worth picking up; especially on a character that attacks once or twice per round (you can spam maneuvers and probably not run out). And Fighter 3 is a fine place to stop cause hey, technically you'll still reach Sorcerer 17 for the level 9 spell slots.
I think being a dex focused character is fine for this--Draconic bloodline sorcerers can have 13+dex AC, which assuming you raise dex to 20, reaches 18 AC, 20 AC with a shield. HP will be a little low for a front-line character, so having a shield is probably desireable. Obviously, going fighter heavy armour and strength based weapons are an option. But they're not even that great. (Two handed swords get up to 8.333 average damage with the appropriate fighting style. A one handed dex based rapier with duelist is 6.5 average damage. When most of the damage comes fron the cantrip, I'll take +2 AC over an extra 1.866 damage).
Optimising hard for race...I think you'd want Variant Human for War Caster, just because your ASIs will be pretty delayed. That said...Half Elf lets you start with 16 Dex/Cha/Con, while a variant human would have a 14 in one of these (Con or Cha). Once you get to the first ASI, Half Elf gets warcaster, Variant Human gets 18 Dex, and still has that 14 in another stat. But the 18 dex is pretty damn important (+1 AC, +1 hit, +1 damage). So mmm...variant human sounds better TBH. With all that being said, variant human does technically lose you 2 HP cause you can't take level 1 in Fighter (spellcasting is a pre-requisite for War Caster).
What stat would it sandbag between Cha and Con? Not sure, actually. With Cha...it does represent damage with Green Flame Blade (baseline, and you get to add more Cha at level 6) and obviously it makes your spells better (although you might be focusing on spells that don't rely on Cha, like polymorph and haste). Still...you presumably still take Fireball? And 14 Cha vs 16 Cha is a decent upgrade on a Draconic sorcerer's fireball. Con represents HP (which you need more of, due to d8 hit dice from Sorcerers), and concentration saves. Things that will come up frequently, although it's not a massive bonus to either.