A tall person fits well on a 250cc or 400cc supermoto, but their narrow seats are not comfortable for long trips, and the 250cc supermotos are best at 65 mph or below. The 400cc Suzuki supermoto has a very good suspension, but it is a lot more expensive than a 250cc or 500cc Kawasaki Ninja with their lower budget suspensions and wider, more comfortable seats.
The 650cc KLR Kawasaki dual sport is good for people with long legs for long trips, but it is a little too heavy to be the best beginner bike, although the amount of power from its single cylinder engine is good for a beginner. It also costs a lot more than the 250cc Ninja, to pay for its better suspension.
For other bikes, it is best to move the stock handlebar ends higher or get different handlebars, and buy a kit to move the footpegs more forward to fit long legs better.
Before buying any bike, have someone hold it up for you while you sit on it with both feet on the footpegs for half an hour, to get an idea of how comfortable it will be for you on long trips.
If you buy the most recommended for beginners 2008 or newer 250cc Kawasaki Ninja, adjust the handlebar ends higher and go to cyclecontrol.com for a footpeg relocation kit. When you get these relocators, switch sides for them and put them upside down, so they put the footpegs lower and more forward for long legs, instead of the standard way for higher and more rearward footpegs better for racing. I think the water cooled 500cc Ninja is good for taller or heavier beginners, but it has older styling.
I am not fond of the 500cc Suzuki- its air cooled engine is sometimes hard to start, and it is quite low on power at 75 mph, worse than the water cooled 250cc Ninja, but it does have a modern sportbike look with side fairings. I recommend Denso or NGK iridium spark plugs for it, so it starts easier.
My previous air cooled 650cc Yamaha was not fun at stoplights on a hot summer day, with a lot of heat coming up toward you from the engine.