Dark Brotherhood and Thieves Guild help

[Renji]

I'm planning on joining both the DB and the Thieves Guild. The question i have is does it matter which one i join first? I want to join the guild that has the lesser rewards first and then the one with greater rewards like armor and stuff last, seems like it'd make sense doing it that way. Also, at what level should i join the guilds because i heard the higher the level you are, the better the rewards are...is this true?

 

[Ironclad]

I met the thieves guild and was given my 'joining' tasks, before I returned to Riften i'd met and joined the DB. As I entered the Guild I was dressed in full DB dress, no one raised an eyebrow.. haha

 

[Streets]

Spoilers? But you did ask so it can be expected. Dark Brotherhood gear is not leveled. Thieves Guild gives you Nightingale Armor (best version at level 32+) and Nightingale Sword/Bow (best version at level 46+). It should be noted though that the 46+ version of the Nightingale Sword is actually the worst version because it can't be sharpened like all the other versions of it can. You also get Chillrend along the Thieves Guild path, which levels out at 46+ as well.

Skyrim:Leveled Items - UESPWiki