I am a HPS man through and through - So I would say 1000w HPS would be great! I would get an adjustable ballast, so you can go from 250 / 400 / 600 / 1000w
a 600 hps with a quality bulb (such as Sunmaster or Hortilux) will produce buds just as dense as a 1000hps. the reason is you can get the 600 closer to the plant than you can the 1000. i use 3 x 600hps and my finished product is as dense as my friends buds grown under 1000 watt lights. also you will want to consider heat build-up in your 4 x 4 tent. a 600 hps will make your life so much easier.
You must be using cheap Chinese led's. If price isn't a factor, I suggest Quantum Boards - 480 watts would suffice - or at least 600+ watts if you use HID. Don't bother with CFL's if you want rock hard buds - they're only good for early veg. Even with perfect lighting not all plants will produce dense nugs - even if it's the same strain.
If you go with a 600 you will need supplemental lighting for the edges as 600 isn’t quite enough. The buds right under it will be grade a. Like Mick said, quantum boards is where it’s at. 4- qb96elite v2 engines, 2- Meanwell HLG-320H-54a drivers, some aluminum angle, 18 ga wire and a plug end and you are in business. About 700 watts draw for $650
Quality led is the way to go but if ya can’t afford it I’d rock a 1000hps aircooled if ya can manage the heat .