Route from Phoenix to Florida

I went from Los Angeles to Orlando all on I-10 but by passed Phoenix. Worst traffic I saw was El Paso and worst roads were in LA. 45 ft Monaco towing a 32ft enclosed trailer. That was last year and I am now 80 years old so if I can do it any one can. Safe travels.

Plugging in Phoenix to Talahassee (even if you are going further, you will pass by there)...There are 3 routes that are less than 1% difference in total miles.
- I-10
- I-10 to I-20 to US-49 (You could take I-49 but then you do add around 50 miles)
- I-40 to I-20 to US-49

The difference is little more than a rounding error, so just about anything could push one way or the other. All depends on what you want to see.

Maybe head out on one and come back on the other so you get to see different areas.

I-10 is the most direct and San Antonio and Houston are not a problem if you avoid rush hour. It does have a number of construction areas between Beaumont TX and Lake Charles LA and west of Lafayette La that can get backed up. Also east bound at Baton Rouge is best done on the weekend because of the single lane area at the Mississippi river bridge.
I-20 is still extremely rough in the Shreveport - Bossier city area.

You would need to reverse the route that we took to Monument Valley (easy to adjust for your start point) to avoid Dallas/Ft Worth.....no regrets.

I-75 N to I-10 west
At Mobile take 98 to Hattisburg
49 to Jackson
I-20 to 69 at Tyler, TX & to avoid Dallas/Fort Work continue on 69 to
82 west at Denison, TX
287 at Wichita Falls to I-40 at Amarillo to Albuquerque to Gallup, NM
(plenty of secondary roads to take to avoid Albuquerque if you want)
264 to 191 north to Kayenta, NM then
163 north to Monument Valley, AZ

I go I-10 myself but remember to take I-12 for the short distance above New Orleans
bumpy

I would choose the Dallas route. I-20 bypasses the worst of the DFW metro mess on the south side. Go thru during the middle of the day (10 am to 2 pm) and you most likely will have little to no trouble with traffic. Unless, of course, there is an accident or doing road repairs.

In Shreveport/Bossier City, take the I-220 bypass around the north side. The stretch of I-20 thru Bossier City was the roughest highway I have ever traveled on 2 years ago. Maybe someone who has traveled thru there recently can say it has be repaved.

Could it be that I-10 is direct to the "panhandle" while I-20 takes you further north just to come back south? Both planners will give you the option of selecting I-20 and swinging back to the 10 anywhere you pick, but unless you tell them you want some roundabout way, they pick the closest, fastest and easiest route.

If you are retired and/or not in a hurry, go through Dallas! RVers don't need to always take the best, shortest or the fastest route.