I would go for Sir Pigglesworth. He has great drops. Including the occasional gem (very rare) and energy (also rare).
Having all 3 fruit trees (apple, lemon, orange) will let you do that fruit trade when you unlock it.
There have been Black Friday sales, good ones too. But I didn't buy anything until last year and have been level 50 for several years. A second wizard school was my goal I think after Sir Pigglesworth. Can never have too much energy.