tl;dr: Get the O'Connell TKO (though I haven't used it, conceptually it is a logical improvement to the current baller head injector/diffuser lineup across the board, the way it is built the plant material is closer to the heating element so you can get similar effects at lower temperatures, which means less harsh vapour).

I personally went the aliexpress route, with some DIY bits and bobs, mainly because I am in Europe and am on a budget. My favourite head I own is the Tiodw Mini, which is a titanium enclosure. I prefer a lot of airflow so I use the larger 4mm balls. The store I buy from is b2cvape, their newest head is the Tiodw Mini 2.0 (which is a hybrid injector and diffuser baller head). It will probably be my next purchase. But with this route you also need to buy 3mm or 4mm rubies (made from corundum), a 20mm coil, a PID and a bowl (the new head is both an injector and a diffuser so getting 2 types of bowl is a good option), a handle (not 100% necessary) and some sort of bong