Tough choice, there are many that would make League a lot more interesting. Some just couldn't even work since there are no trees in LoL, like Nature's Prophet and Treant Protector. However, my top 10 would probably be like:
- Doom
- Chen
- Razor
- Dazzle
- Bloodseeker
- Undying
- Rubick
- Bane
- Tusk
- Underlord
https://d1u5p3l4wpay3k.cloudfront.net/dota2_gamepedia/thumb/4/40/Doom_icon.png/150px-Doom_icon.png?version=c8252a23424ec63b5e3a8c9ccedcfcd6
Doom is a really fun character to play as, maybe not against though. I feel like LoL players aren't ready for a 16 second silence, true damage DoT that also disables items and could even disable passives once upgraded. Not to mention his gold income would be pretty dang game breaking. I think there are other heroes that people would complain about more, but Doom would definitely be up there. If people hate Malzahar... oh boy.
https://d1u5p3l4wpay3k.cloudfront.net/dota2_gamepedia/thumb/6/61/Chen_icon.png/150px-Chen_icon.png?version=1678ad4f149a9591a8b78c05145a9008
Chen would actually be a pretty fun person to be in LoL. Have the Jungle become your army and invade lanes with your army. He would really shake up the Jungle meta, that is for sure. He is similar to Ivern, except he is more offensive oriented overall. Plus, since LoL monsters don't have abilities, the most frustrating part of learning him would be cut out. Decent choice.
https://d1u5p3l4wpay3k.cloudfront.net/dota2_gamepedia/thumb/6/66/Razor_icon.png/150px-Razor_icon.png?version=3f740cba70e4907e9f2382956bd935f9
Screw your ADC. Screw your Yasuo. Screw everyone in the game that makes people get frustrated in LoL. I take all of your AD and then punch you in the face with a non-projectile ranged basic attack. Get out of here with that screwy stuff.
https://d1u5p3l4wpay3k.cloudfront.net/dota2_gamepedia/thumb/e/e6/Dazzle_icon.png/150px-Dazzle_icon.png?version=a9b9de284d02c96bf611c4c2fe58e92e
Dazzle is a really fun Support. Simple as that. His Shallow Grave would also make the whole ADCvAssassin fight a bit more interesting at times.
https://d1u5p3l4wpay3k.cloudfront.net/dota2_gamepedia/thumb/5/56/Bloodseeker_icon.png/150px-Bloodseeker_icon.png?version=c0fb65a1857480e1f03dc981fcf73c03
Entirely for the speed memes. If you think Rammus is fast, try this guy out for size. His Thirst passive removes movement speed innate penalties and then gives him super speed when someone is low. He would be a nice Jungler, although I think people would complain about Rupture a LOT!
https://d1u5p3l4wpay3k.cloudfront.net/dota2_gamepedia/thumb/6/61/Undying_icon.png/150px-Undying_icon.png?version=e240f119a099122f1b77bed8603a4096
In Dota 2, he is an actual person who can 1v2 early game, so he could shift the meta just by existing. Duo lane against an enemy ADC and Support? Nah. Just throw Undying down there and watch them cry as he takes advantage of their weak bodies. Throw down a Tombstone and watch them cry as they can't enter lane for the next 30 seconds or risk being shredded.
https://d1u5p3l4wpay3k.cloudfront.net/dota2_gamepedia/thumb/8/8a/Rubick_icon.png/150px-Rubick_icon.png?version=16634f6e0e34461eae62c2b162546eda
I don't need to explain this. Pretty sure everyone knows about Rubick. People have been asking for a champion like him to be in LoL since the stone ages. He would make for a funny Support champion (yes Support, Rubick even in LoL I feel wouldn't have enough damage to be considered a Mage).
https://d1u5p3l4wpay3k.cloudfront.net/dota2_gamepedia/thumb/c/c3/Bane_icon.png/150px-Bane_icon.png?version=fe82962b3226b7e75d9be4ea1ad29f69
Same as Razor.
https://d1u5p3l4wpay3k.cloudfront.net/dota2_gamepedia/thumb/c/ce/Tusk_icon.png/150px-Tusk_icon.png?version=b8b09a15442d11c5151e85677828a29d
Tusk is just fun in general. Imagine Vi, except based entirely around landing a single basic attack that deals 350% damage. That's fun as hell. Not to mention his Snowball would make the Bottom Lane really interesting. He might actually be a balanced champion in LoL haha!
https://d1u5p3l4wpay3k.cloudfront.net/dota2_gamepedia/thumb/1/18/Underlord_icon.png/150px-Underlord_icon.png?version=8d0c1c61e612253a0eff6c9a2f73ebc4
Same as Razor and Bane, but with MORE! He would be such a fun character to base a team around. A Super Siege team that just zones the enemy out for a long time in order to get their tower. Again, he might actually be a balanced champion in LoL, albeit with some tweaks.
Bonus goes to:
https://d1u5p3l4wpay3k.cloudfront.net/dota2_gamepedia/thumb/f/f3/Shadow_Demon_icon.png/150px-Shadow_Demon_icon.png?version=98e44c29561f30883844168d05e3e35e
Cause who doesn't want to abuse his E in LoL?