I have zero experience with motors on bicycles. I am just getting into this sport.
Lots of experience with motorcycles, 2-strokes, and 4-strokes.
2-stroke - Lighter, cheaper, simple, good power/weight ratio.
4-stroke - Heavier, more expensive, tends to be more reliable. You need 50% to 100% larger motor to get the same power as a 2-stroke.
Mixing gas and oil is no big deal. Unless you don't have the oil. If you're one of those types that buys gasoline when the car is on "E" empty, maybe 2-strokes are not for you. Or you can carry a bottle with 2 oz of oil. Put in some gas, some oil, more gas, put on the cap, rock the bike, ride. I have 2 gas cans for 2-stroke premix, 2 gas cans for 4-strokes and cars.
NOISE - Here is a real key item. Young riders often want "Hey look at my loud bike!" (Dig me riding!) Loud motors are more powerful! Loud pipes save lives! I've been riding motorcycles for 40 years, I still get mad when some moron goes by with loud pipes. It's just bad for the sport.
The truth is loud motors anger a lot of people. I'd rather have a quiet bike that is more stealthy. Almost every off-road riding area I used as a kid was closed down due to noise complaints. Now you want to ride a street bike out of your neighborhood every day, I suggest making the bike quiet.
I have a 2-stroke motor from a busted weedwacker, that runs great. So my first bike / motor combo will most likely be a 2-stroke. Making it quieter is going to be a challenge.