Below, I am comparing apples to apples in PRICE only. The Minelab GPX's are out of my league expense wise, and I don't nugget hunt.
The TDI is a great unit, and you can set it up to just low conductive hunt and not be bothered with clad or most iron ( but you will miss silver). It can also clad and silver hunt while eliminating most iron but also it will eliminate low conductors too like nickels and gold jewelry. I took my TDI ( not Pro model) it to a park yesterday and using the 7.5 inch coil, picked up several quarters, dimes and copper pennies among tons of aluminum trash and iron nails. Using it in parks and on land, the discrimination level is a all predicated on how you set the ground balance and pulse delay.
Thing is, I also have an Infinium, and use that more on the beach because of one specific reason...it's WATERPROOF.
Remember...beach means water, and if you end up getting near it, especially salt water, you are much better off with a waterproof unit due to the simple facts: it will not get fried if dunked, the salt water, salt air and sand will not penetrate into the control box, and you can rinse it off completely when finished hunting. It does have tone ID, but it is always active, so you will always hear a hi/lo or lo/hi on targets. You can somewhat gold hunt and only dig hi/lo signals, but it does not have the discrimination capabilities of the TDI, so it is much less a land/coin hunter if you wanted to use it as one compared to the TDI.
BUT...the TDI is an awesome wet sand unit so if you want to hunt low tide areas, you will be 'kinda' safe in that the unit is not subject to being dunked under water if you lose your balance or accidentally fall and the control box hits the ground.
So, for land, wet sanding and nugget hunting, the TDI is probably the better choice due to a lot more coil selections and the fact it has a conductivity switch and the ground balance can act as a raw but effective discriminator.
Suds and water...no brainer. Infinium because it's waterproof. But is no slouch as a nugget finder too.