Flathead and spotted sucker questions.

For flats, try shallow water near deep holes at night.  Most of my luck comes from slacker water.  If you can run several lines where you live, try a line in the core of the hole and one or two on the breaks. It really is dependent on time of year too.  They can be in both places sometimes. But I would concentrate most efforts around the deepest, most wood laden holes available. 

For the spotted suckers,  patience is the key.  Almost like fishing quillback from what I've heard.  I've heard groundbaiting can be effective.  But I would sight fish them if you find them.  I've seen them on the Perdido River before milling around in the cypress roots, picking art micro-organisms and such.  No luck with my offerings that day.  I bottom riged crawler quarters and halves around where I saw them, and only caught some blacktail redhorse and sunfish.  Tried several times too. 

We were just talking about spotted suckers this weekend. 
I fish for them almost the same way I fish for quillback. 
The key is getting your bait to them and keeping all other fish away. 
Thats the trick. 

My first was a fluke. It was just finished spawning and was sitting next to a metal pole driven into the bottom of the river from an old dock. I thought it was a funny looking white. i dropped my bait in and moved it close to its mouth. It moved up and ate it and bam. Easy. 

The second one was during the contest a few weeks later. I stood in one spot waist deep in the river for 5 hours wihtout moving. not exagerating. 5 freaking hours.
In that time I made a point to catch every single baby perch in the county. Once I had them cleared out my bait could sit still un bothered for a short while..... About 30 min really before the spotted sucker slowly moved forward and slurped it up. 

Third was similar to the first only I only stood still for an hour. 

Fourth had me sitting for almost two hours fishing for one spotted sucker in a brush pile. he finally aproached and slurped up the waxworm. I fought him for about 20 seconds before a 3 foot musky shot out of nowhere and went right between my legs to destroy the sucker. The musky got scared when he realized I was there and spit the sucker. The sucker sank and died and I didnt catch either and I wasted 2 hours. 

What I am getting at is they are one of the most frustrating fish I have ever fished for. I always say Ill never do it again and nearly every year I find myself trying. 
Small bait! Smal hook and light line.
I havent triend the micro hooks yet, but this next summer I may try them for both spotted and carpsuckers. I am betting it will work much better. 

Another thing that makes spotted suckers evil is their ability to suspend. In one river I see them often in large schools 30-50 fish forming a ball about 6 feet wide. They sit in the middle of the water column in and around log jams and brush piles. I hate them...

Look for slow moving backwaters with brush and weeds. Then find small clearings in thsoe weeds. Then the fun starts.
As far as spotting spotted suckers. they look very similar to whites under water. white suckers normally have a clean noticable line where their scales start and stop at the base of their head on their back. Spotted suckers have a subtle transition at this point and the line is barely noticable. In addition to that their pectoral and pelvic fisn are lightly mottled like a hogsucker. 
learning to ID them in the water will help a ton in catching them. 
 

Knuth,

Are spotted suckers more frustrating than carpsuckers? Is that possible? 

Much much more so. At least carpsucker have tiny mouths. spotteds really have no reason to be such a pain.

Actually I think the main frustration is the habitat. Its never easy to get to them and the water is rarely clear and the area where they live is normally covered with tiny perch or gills. Carpsuckers seem to be in the open more and alone.

Well... I guess that is why I drink. Next year.... Next year I will get a spotted in Minnesota.