Python offers you possibility to go anywhere and anaconda requires large pad, therefore python gives you more options for trading. I'm missing my python when it comes to the trading, however if you have a solid trade route for the big boat, get it. Also keep it in mind anaconda is a true battleship and handles as such. Most likely you'll buy another ship (just for having fun) shortly, since trading anaconda might be too boring. This is what some anaconda pilots do. You can also get type 9 for trading, it's cheaper and it takes 500 tons, and something else for shooting.
Having recently traded up from an A-grade Python to a D-grade Anaconda, I have to say I won't be going back for trading or combat. The Anaconda is much more fun to fly, the fat ass and double-duration boosts make drifting it around everywhere fun. The lateral and vertical thrusters are way better than the Python's, it may not pitch as quickly in numbers but it
feels nippier even for such a large ship. Mine's rigged to haul 476 tons with a class 4 shield generator and a few pulse lasers, and that's more than enough for some nav beacon shenanigans when my trade route gets boring. Still gets 20Ly jumps even when fully laden, and if I wasn't so afraid of taking a 10 million credit hit to the wallet I'm pretty sure I could boost it out of the letterbox sideways. Outposts tend to dry up too quickly for the Python to make decent money off them anyway, better to hunt down deals in larger starports if you're going for volume.
One thing though, I'm sure mouse-using conda pilots have noticed this before but I haven't seen it mentioned anywhere. The little yellow square that shows your mouse aim position, it's in the exact middle of the screen on every ship with a centre-aligned cockpit, but on the Anaconda you actually sit above it, and for some reason this dot hasn't been moved at all. The dot is actually slightly below the point where my ship's nose is aiming from this point of view, and I can no longer use it as an orientation marker to line up my approaches, else I end up aiming slightly above the target when I get close. This confused the hell out of me at first because I'd point the dot (which I assumed was still dead centre) at my destination in supercruise, and constantly have to tip the nose back down to stop it aiming further and further off-target as I got closer. At first I thought it was a quirky orbital feature of the station I was flying to, until I went elsewhere and it was the same. I've since figured out the "sweet spot" just above the aiming dot where my ship is actually pointing, but this thing is going to bother me forever until they change it.
I wish they'd just give us velocity vector markers (prograde/retrograde at least) on the HUD. Helpful to know when you're not flying perfectly straight too.