After 22years rated on type I should say 737, but . . . for the moment, Boeing are dithering on new engine/new aircraft decision. Meanwhile Airbus are racking up orders for A320Neo.
If I had to spend the money (even if I don't "really" trust FBW Airbus
) I would be forced to say Airbus makes more sense, considering also that you will be half -way, or more , to being A330/340/380 rated.
As previous posters said, 500hrs on type is the generally accepted/demanded minimum, so don't buy any rating without a conditional job offer to accompany the expenditure.
That is a mugs game, do you realise how many 737/A20 pilot without any experience on type have been fleeced these last few years ? believe me there are a fair few around.