If there will ever be a need to wash a load of laundry and take a shower consecutively, you will have greater satisfaction if you don't run out of hot water.
Running out of HW with only a 30 gallon tank is more likely in the land of cheese than in the warm swamps of Florida where incoming water temps in winter are 30F lower than typical FL temps, but neither is in great danger with consecutive washer + shower draws. A 10 minute 2.5 gpm shower @ 105F with 35F incoming water uses ~20 gallons of 120F water, but with 65F incoming water it's only ~18gallons. If the storage temps are 125F the HW volumes are lower 120F is something of a lower-limit. If your shower head is only running 2gpm (about where many 2.5gpm-rated showerheads actually run except in high water-pressure areas), it's more like 16 gallons in cold-water country, 14 gallons in FL.
A clunky full-size old-skool top loading washer will use ~40 gallons of water, but not all cycles need to be hot water- a warm-wash/cold-rinse will draw ~8-10 gallons from the HW tank, but hot-wash/cold rinse will draw 16-20 gallons from the tank. A water-sipping mid-size front-loader will use roughly 1/3 the hot water of a top loader as long as the rinse cycle is cold: 3-4 gallons for a warm-wash, 6-7 gallons for hot-wash. It's not as favorable if the rinse cycle is warm or hot (since more water is use in the rinse than the wash cycles on front-loaders) making it more like 2/3 of the hot-water draw of a top loader on similar warm/hot settings.
With either a hot wash/warm-rinse front loader or warm-wash/cold rinse top-loader followed by (or concurrent with!) a 10 minute shower scenario the 30 gallon tank keeps up in FL but will fall short in WI. And a hot-wash/warm-rinse with a full sized top loader would be an issue for taking long showers even with a 40 gallon tank. (With the slow recovery rates of tanks, it's possible to do-in almost any sized tank if you work at it, as teenagers all over America prove daily!
) First hour ratings on 30 gallon tanks are tyically in the ~45gallon range, but 40 gallon tanks are only in the mid-50s, only 20-25% more, not the 30-35% more that the storage size might imply.
And of course, taking the shower first, letting the washer use the possibly-tepid water is still an option if it falls short. A 10-25F reduction in temp at the middle or end of the cycle is a disaster in a shower, but not so much for a washer- the hottest water would be used for the wash, even if the warm-rinse ran tepid. And again, in warm-water FL the transition to cooler-water at the end much less jarring than in frigid WI.