Fished both places many times and both should be great fishing end of May. If you go to Sakakawea, the Van Hook arm is hard to beat that time of year. B-bouncers, jigs, cranks, live bait rigs - all will work depending upon wind, weather, water conditions, temp, etc. Devil's lake will be good end of May as well. Same presentations, maybe more casting and/or pitching presentations on Devils. Big water - big waves and strong prairie winds very possible in the spring. Count on a wind day, just like a great lakes trip. Personally, with limited time, I would pick one, and learn it. It may take a day or two to figure the bite out and just when you get it figured out, you leave. Just my opinion. Have Fun & Good Luck!