It depends on the battle system and what you do while you're grinding. Grinding is tedious per definition as far as I'm concerned but if combat is fun and varied and you don't have to go through hours of stupid animations before and during battle then it becomes bearable. Some kind of auto system helps a lot. I'm currently playing Bravely Default and grinding in that game is, well, boring. Thankfully you can use auto combat and raise the encounter rate and battle speed, which does wonders, especially when leveling up jobs (which makes up about 99% of the grinding I've made so far). Just move the stick a bit, get into combat and have the game do the rest while I watch some Netflix. Though I'm not entirely sure if "Hey, at least I can Netflix while playing the game" should be counted as a positive.
I really don't like grinding in games that require a lot of input. I quite enjoy more action-oriented battle systems such as the ones you find in Tales of and Star Ocean, but they can also make grinding much more annoying. In some games you're rewarded with extra XP if you do well, which imo is a requirement in games with more "demanding" battle systems.
In Xenoblade Chronicles and X I really never felt like I was grinding because there was so much to do and so much to see and leveling-up just kinda happened. 
What I usually have a much bigger problem with is farming for items. While grinding for xp wasn't an issue for me in Xenoblade I had a much bigger problem with gathering materials. In X you could equip certain missiles that targeted appendages, which really helped you get the materials you needed, but it was still a problem. You had to respawn enemies and the game was hilariously unspecific with were to find collectibles (the item is found somewhere on this huge continent. O....K) so hunting those was a real pain in the behind.
Then you have games that takes bad grinding to entirely new levels. For whatever reason I decided to do a 100% achievement run when I played Final Fantasy XIII. I know, it's a fate worse than death but on the bright side it completely killed the achievement hunter in me. The end game in FFXIII is a disaster because it's all about battling a few types of enemies over and over and over and over, and to win you have to make use of the paradigms, which increases the button presses you have to do, and then you hope that you're lucky enough to get the item drop. There's zero variation, it's just rince and repeat.
My absolute worse grinding experience however was in Hyperdimension Neptunia: Rebirth1. And it's not really because the game requires that much grinding but because it forces you to see all of the awfulness the game has to offer (for the record this is one of the worst games I've ever played). The game rehashes levels in ways that I didn't think was possible (a new level in Neptunia many times means a direct copy of a previously explored level. And the Neptunia way of making a level with two rooms sometimes means taking the first room and switching the entry and exit. Yeah). Levels, that from the very beginning are some of most uninteresting, uninspired, most awful ones I've ever had the displeasure of "exploring". Those sets the stage for complete horribleness. The only positive aspect of Hyperdimension Neptunia (I honestly can't think of another positive) is the numerous costumes you can craft for your characters, which is cool because I like character customisation. Unfortunately crafting dresses requires items, which means you have to go to those #@&%! levels and farm for items. To make matters worse Neptunia, like Xenoblade, has collectibles lying on the ground everywhere. And the collectibles you actually want are obviously rare as fudge, which means you have to run around in those...places, pick up items and pray. I actually spent like 60 hours on this mess because I'm stubborn and stupid and really like seeing low-polygon anime girls in swimsuits but after starting to question the meaning of life I managed to stop.
