Which used water damage iPhone to buy?

Looking to mess around with iphone logic repair and potentially using the phone. Starting at a iphone 6s. There are two iphones which of these symptoms should I stay away from buying. 1st one when connected to charger starts overheating around top end of the phone. 2nd one when plugged in has no difference. Would the first one be a better buy because this shows charging port is working (potentially processor damage) OR the second one which doesn’t produce any heat but the water damage could be less severe to repair? Thanks.