If I were you I would go for a high and deep tank with a low waterlevel. (incase of escape)
I house mine in 5 x 2,3 x 2,3 ft tanks. But I will go bigger in the near future. (6x3x2,3)
(maybe in a year of so)......but if you go for an annectens and buy it small it will be fine in a 4x2x2 for a long time.