Hosokawa is the best positioned out of all the Daimyo's I've tried.
Suo is okay, the problem is Korea will usually ally with Harima and get on your case and having your armies split in two if you can't guard the South Korean Sea is killer. Their trade dominance is unmatched, however, thanks to their starting fleet of Light Ships and owning a trade hub.
Harima is also another okay choice but I couldn't see much success with them.
Japan proper is actually pretty hard to play if you're rushing for unification, because you're in the middle of a bunch of power hungry Daimyos. The safer option is to take over the southwest end while the northeast end fights among itself, and then take Japan (the current reigning Daimyo, not the entire country) in one fell swoop during an opportunistic war (when they are attacked or when they are attacking someone else).
The single province Daimyos aren't worth talking about although you'll have your work cut out for you if you try to take Takeda by brute force.
The CPU sees a lot of success with Shiba but I personally wouldn't use them because their provinces are all split up and I hate taking away light ships from trading just to protect my transports.
You'd think Uesugi would be good but I actually had a really hard time with them. I think it's because their closest neighbors, Takeda and Mutsu are both highly defensible, and that it's impossible to get to Kyoto unless you have military access through Hatakeyama, Takeda (although you can ally Takeda immediately) or Suruga, which can be hard to get when everyone is scared shitless of you. Uesugi's sea force is kind of bad, and their land force is only equal to Japan's.
Hosokawa's situation summarized:
+ Four starting provinces
+ Good navy and land force
+ Close neighbors no one cares about (Bungo, Satsuma, Hatakeyama)
+ Close to the heart of the Nippon trade node, meaning you can dominate trade as part of your opening conquest
- Tends to get into trouble with Korea (all the southern Daimyos do, however)
- Poor allies, I believe they can get Bungo and Takeda at the start, both of who are totally useless
- Total territory divided by both sea and land although this is mitigated by their superior force
- Near Japan. Basically, whoever takes Japan first is not going to be friends with you, so it'll take some patience to wait for them to calm down and turn their sights northward before you can strike at their weakened rear.
My record for total unification was around 1500, I believe, and that's only because I opted to go for Annexation of some inopportune vassals (back then I didn't realize how time consuming Annexation was). Which I assume is decent, considering Oda didn't dominate Japan until the 1580s, so I have at least 80 years over Japan's greatest general.
Starting as a Daimyo can be pretty complex but it's how I started EUIV and it's a great way to learn the intricacies of naval management, coalition, vassals and trade, all of which are extremely important in this game. Sort of a trial by fire thing.