This would be my suggestion…
Try the
Tamiya M4 Sherman. It’s an easy build and being (mostly) Olive drab in colour you can have fun with fading, washes, weathering etc without the added complication of a 3 colour camouflage finish of say a late war Panther or Tiger. In this way you can have fun experimenting a little and concentrating on trying some techniques. Also, because the Sherman has ‘live track’ the vinyl tracks will look acceptable straight out of the box (after painting them).
Obviously a great deal of this will come down to whether you like the look of a certain tank or not, but from a practical point of you this would be my choice.
Tamiya M4s are also relatively cheap!
Paul