The answer is......it depends.
What is you playstyle? I find a strength build is easiest for most people the first time playing. Once you have, say, 20 in vigor and endurance, I'd focus on getting strength to 40. If you find yourself running out of stamina or getting hit a lot, add more to vigor and endurance. Maybe take dexterity to 18 or so, to give you a little leeway with weapon choice. Give enough vitality to support your equipment choices.
Whatever build you decide on, this is a game where a certain amount of min/maxing will help; if you aren't using magic, don't bother with intelligence or faith. If you aren't using heavy equipment, vitality is a waste. You CAN respec your stats eventually, but only 5 times per play through, and you need a covenant item to do it.
The raw infusion is OK early, but if you go full strength or dexterity, you'll want to infuse with either heavy or sharp. Or refined, if you choose to do a quality build (40/40 strength and dexterity).
Nothing wrong with the broadsword, but I'd argue the longsword has a better move set, worth the slight reduction in damage. You can also farm Darkwraiths for the Dark Sword, arguably the best straight sword type weapon in the game.