My favourite coil for general use, would be my Cors Scout. I find it a good compromise (?) of coverage, weight, balance, sensitivity & accuracy in pinpointing.
Other coils in my collection are Teknetics 5", great in hard stubble & trashy sites, 8x6 SEF, good in softer stubble & taller grass etc, Cors Cannon, a tad on the heavy side, but for cruising pasture land, ideal. Kinda hit & miss on pinpointing though.
Had a Detech Ultimate 13" for a while, but it gradually "faded away", as in it lost it's effectivenes over a period of time. I didn't realise there was a problem until one frosty day. I used the Ultimate in the morning, didn't dig much, then swapped to the 8x6 SEF at lunchtime. Immediately the field came to life. Walked over the same patch as I'd walked earlier, and within a few minutes I'd dug a couple of musket balls and a Bullhead Sixpence. Later checked the screw connector for loose/broken wires, but couldn't find any faults there, so assumed i must be an issue within the coil itself. Great coil I thought, but the reliability concerned me. No one seemed willing to attempt a repair, so it got binned. Replaced with the Cannon.
Bought the T2 used, and found it rather noisy........................... Turned out the stock coil was goosed. That was when I got the Ultimate.