Warframe's Solar system got updated, and since the last time I played, Draco was the best place to level up all your gear. What's the new place where people grind for levels? Some strategy and explanation would be a great additive.
There is still some debate over a few locations in the community, but a node on Eris called Akkad is generally regarded as the new "Go to" place for leveling frames and weapons. It is a dark sector defense mission, which also means more xp and more drops than usual, which are some of the reasons it is so popular now (all of the neurodes!). Some locations in the now open void are also regarded as good leveling spots.
Be warned, however. No spot in the game is going to be as good as Draco used to be (DE wanted us to take longer to rank things up, which is why they nerfed Draco). So don't go into any of these missions and expect to level up something from rank 0-30 in a single run with such ease anymore.
Edit: in dark sector defense and excavation missions, I highly recommend a repelling bastille vauban to protect the pods. Although this strategy really only works in groups, since Vauban is so squishy.
The new "Draco" is Berehynia, Sedna. The usual composition involves Trinity for EV, Rhino for buff (Equinox is the other viable option), a leech with Corrosive Projection aura, and a DPS such as Sayrn with Spore build or Banshee with a Resonating Quake build (other viable options are Divine Spears build Nezha and RJ Excalibur with specific positioning).
Akkad, Eris is the new easiest place to gain affinity. There are a plethora of ways to do so including various AoE/damage builds (Ember, Sayrn, Banshee), or unlike Draco, AoE weapons that will work as well (Synoid Simulor, Nightwatch Napalm Ogris, Kulstar).
Personally I have been running a speed Nova with Justice Blades equipped, however, I've also done runs with an Ember just standing on the crates and dumping Synoid Simulor fire at the Defense Pod.
If you keep yourself to a minimum of gear and run an affinity booster, 20 waves should max out any item excepting perhaps a frame. The real trick is getting a group to stay through 20 waves. Most public groups seem to be credit farming and will leave after 5 rounds.