Well, I don't claim to know everything about every detector, but in most cases if someone wants to hunt in heavily infested iron places he needs to own something with at least three of the following. The more of these toys he has, the more likely the machine will work well in soil filled with a lot of nails, BUT a high gain one will often defeat the purpose.
# 1 High frequency continual search (over 10 K, and not a multi-freq one)
# 2 A CONCENTRIC coil. Not a coaxial or DD. VERY important!
# 3 8" or less in diameter. A 3" coil would be just about ideal.
# 4 Low gain (not running full power all the time)
# 5 A choice between automatic and manual ground balance built into the detector
# 6 EXTREMELY fast auto-retune (auto return to ground balance) recovery time
# 7 Very fast auto-threshold
There is still much debate as to whether a 2 filter, 4 filter or 6 filter works the best, because it really depends on how the circuitry is designed.
A Fisher 1236-x has a very well praised iron blanker (it lowers sensitivity) and is one of the very few that has #5 ratings across the board all the way, on Metaldectorreviews.com. Most Minelabs have iron blankers too but with so much gain they may still have too many troubles with too much linear scrap such as nails, screws and wire. White's and Minelabs have determinants to display how much iron is in the soil or is in a target, but that does not help in canceling all that noise. An MXT has some real problems in that area but a DFX does not have as many.
A 1270 has so much #$%$^% power in it (so does the Tejon) that they are absolutely overwhelmed in high magnetite and high hematite soil. So do Nautiluses. They do well in hunting relics because of all this power but they also have a lot of troble with a lot of nails, etc when used with full power, and bad soil makes things even worse.. Yes, the 1270 has an iron blanker too, just like the 1236, but it must have it's main sensitivity pot turned way down in such cases. In doing so, it nearly matches the 1236 in it's behavior..
If you want to see something that works fairly well in trashy areas get a cz with a digital screen, because it has a bit too much discrimination built into it to begin with. Turn the sensitivity down, cancel iron completely, notch out foil and do not dig anything that gives a double-blip or that has an elongated response one direction and a short one the other. Anything as big as a coke can or nearly that size or closer will always give a bell te;ephone sound on my cz-70, but it still won't beat the discriminating capabilities of the Compasses and some of the cheaper Tesoros overall.
If I were about to buy a new detector for your purposes I would strongly consider a Silver Sabre uMax or maybe one grade up. Get an Explorer or a DFX if you like to tinker and want reasonably good depth and target Fe analysis, or get a CZ3 if you like a real good one for older coins and use them wherever they work the best for you..
Those Tesoros are a lot more detector than they are often given credit for though. They are lightweight, cheap, and get 80% or better of all targets that people with $1000 machines do. They are superior discriminators and cherry-pickers too. MOST lower-powered detectors cancel iron better than powerful, expensive high-gain ones. White's classics, and other White's low-end detectors though, do not. They are very sensitive to linear steel and iron, such as nails. I own one. They do make fairly good relic machines though, in spite of their lack of really good depth.
BTW, an Ace 250 will drive you completely nutZ in that scenario. I used to own one. Notice, this is past tense as in "used to".
If your soil isn't high mineral (iron) I would look for one of the old 100 K's. I have had other brands of old 100 Hz detectors but the Compasses were the best of the best. Most people think the 77B auto (super fast retune) was the best of the lot. You can find one on e-Bay for less than $150 and if it doesn't work well in your soil you can always sell it again for the same money. Many people still know how well those old Compasses were made and still work. Again, I would look very strongly at the lower priced Tesoros.