I took the liberty of turning your post into a poll ;)

I am not a big RPG fan, but my vote is in on the Western RPG side purely because of Ultima VII. Despite being out for about 15 years now I still haven't seen another game world that has captivated and immersed me as much as Ultima VII's Britannia.

Generally I prefer western RPGs, but I actually have to say that Bioware is single-handedly turning me off them these days. If it wasn't for Bathesda I would have probably got stuck into Final Fantasy a few years ago. Everything I liked about Bioware in the past (stats, exploration, party micro-management) has all fallen by the wayside as they are obviously now only focussed on making simplified and more accessible RPGs for consoles. I loved Bathesda's Fallout 3, even though that was also kind of console-ised but it still retained a fairly complex stat and skill system. It also isn't an FPS in RPG clothing like Mass Effect.

I have played and finished the odd JRPG in the past (Grandia 2, Shining the Holy Ark, Dark Savior, Allundra) and I think what really differentiates the two genres, to me, is the line between exploration and combat. Nearly all JRPGs I can think of always transition to a separate mini-game on a smaller-scale screen or play area to resolve combat, while all western RPGs I can think of keep combat and exploration on the same scale. This was particularly evident in Ultima 7, where if you got into combat you could try fleeing if things weren't going too well and your assailants could well follow you half-way across the world map. Compare this to the JRPG where 'flee' is usually just an option on a menu where you might lose a few HP as punishment. I far prefer the seamless line between combat and non-combat - and don't even get me started on the 'random encounters' in the typical JRPG.

I haven't even mentioned story up to now, which I suppose is because it's of a lower priority for me for what makes an RPG enjoyable. For the most part, an RPG story is painfully linear whatever the genre - and if I really wanted a good linear story I'd read a book or watch a movie instead (yes, I know this is going to be the most contentious point, but interactive media at the moment just can't tell an engaging cohesive story).

I prefer old-school western style games. Ie everything pre-dating Fallout 2.

My favoriate things in RPGs are:

Exploration, Combat / Character development Mechanics (Turn-based pref) and Story (In that order)

I haven't played any of the new western RPGs, Morrowind and Oblivion just didn't look interesting to me. I've got a copy of KOTOR and Mass Effect 1, but haven't played them yet. I'm sure I'd like Fallout 3, but waiting to get a 360.

Anyway, I've recently discovered the Shin Megami Tensai games from Japan (And other games localised and published by Atlus)  Available mostly on the DS, PSP and PS2 - They are essentially Eastern-Western RPGs, as in they were originally inspired by western RPGs back in the 80s but are made in the east. So they are a sort of hybrid.

My vote: Western.

I also prefer the old-school style over modern RPGs. They just have a level of depth that is lacking in anything released these days. I'd much rather replay Baldur's Gate 1 or 2 than Dragon Age.

I was never a fan of KOTOR - in fact I think Neverwinter Nights was the last Bioware game that I thought they did everything right.

I love Bethesda RPGs. I forgive them for weak characters and story, because exploring feels great.

KOTOR 2 was my first Bioware game and I forgave it for its unfinished ending and tedious item management because the characters and story were great.

But I could not forgive Final Fantasy 8 for its random encounters and unskippable combat cutscenes. It was my first jRPG and I never tried another one.

Oh man, I've had this talk with my old flatmate many times. He's a huge JRPG fan and I'm a WRPG fan so it made for interesting conversation.

The defining characteristics of each genre have already been noted so I won't repeat them except to say that my personal preference is Western RPG's because I find effeminate men and kawaii utterly revolting.

I also dislike the ultra masculine gears of war characters, and the tits-hanging-out lara croft characters as well.

Most Western RPG's let me make the guy look like whatever I want him to look like which is great.

But yeah, that's just my opinion. I agree that games like lost odessey look good, I just can't handle the ladyboys.

I would like to say, it is also depends on which of the J-RPG or Western RPG you have been grown up with. Often, you tended to prefer things that you've been grown up with just because it triggers the memory of how much you were interact within the game. 

I've been grown up with mostly with J-RPG, but I really would like to agree with Paul in terms of how I realised that Western RPG has its strong sand-box style approach. For example, I haven't been playing many Western RPGs up until Fallout 3 which it just blew my mind away and I've never played a video game like this for a long- time. I was very surprised the fact that Bethesta covered the so many little details and elements synchronising each others very well. 

Regarding J-RPGs, I'd like to agree that they are mostly very simple and linear and I totally agree what Damien had said about how it is very artistic and visual and pushes themselves beyond the stereo typical fantasy perspectives where as the first thing I would come up with Western RPG would be playing games based on texts(classics mostly). The thing with J-RPGs is that, they never stick to the realism, they ignore pretty much everything and I guess that's how it is very unique and different to Western RPG.

I definitely can't say which is better because I like both of them in very different ways. Sure, lately I've been thinking how Square-Enix isn't pushing hard enough with their RPGs which lets me down(hence FF13...God). Though, I must say that both of them have their own very strong style approach and I would like to actually see a video game which the both things synchronising. Playing Fallout 3 like game with Final Fantasy characters and environment would be an awesome game!