I don't have any experience with a Cobra but I do have a ATA T2 and RSST. Between them I think the build quality is MUCH better on the AGA plus it has the option for a glass
tank. The RSST is a little easier to set up with it's spring post and insulated wick hole so there's positives and negatives to both.
The stock air hole is tiny on the RSST way to small imo giving a harsh hit with little vapor but it's an easy fix. I drilled it out to 1.2mm same as the AGA and it performs the same now, I've heard the air hole on the Cobra is very small also.
The wick hole is larger on the RSST, if you're going to use ceramic wicks you'll have to drill it out as the smallest ceramic wick now is 7/64 and it won't fit the stock hole on the AGA T2.
If you want the easiest build that's the RSST with the spring post and insulated wick hole which helps if you're using SS. Either would probably be modded by most but the easist route there is the RSST also as it's much easier to drill the thin top cap than it is to drill
through the wick hole on the AGA.