For longer term wear, the most comfortable plug I have is the LH Glass medium plug, its around 4.5inch circumfrence, so fairly conservative without being too small, plus it has a skinny neck, so sits inside comfortably, unlike the booty buddy, which is about the same size from top to bottom, this gives you limited ability to stop it sliding out.
being glass, you can also use oil / silicone lubes which last longer than the water base ones. I only use LH discover, so if I am planning on having it in for extended periods, need to factor a reapplication of lube.
One downside I have noticed of all plugs is the lube escapes and you end up with a wet patch in your pants. I usually wait 10 mins or so after inserting, then check and dry off any excess liquid on the base of the toy to stop this. Ok if wearing dark pants, but if you are in light pants / jeans etc, you really don't want a wet patch on your bum!
Think about what it is you are looking for from your anal toy, if its a p spot orgasm, then from what I have read, the aneros toys are king of the hill, but, if its just the feeling of fullness / stretch, then a more bulb / cone shaped butt plug may be the go (as these are designed more for long term / stationary wear).
I agree 100% with AmyA, I find the fullness feeling of a butt plug so satisfying and enjoyable that I will often just put one in at night whilst watching TV. You can sort of rock / clench a bit to enhance the sensation, just don't go too big else it can feel a bit pokey on your insides.
Be wary, once you do start to enjoy it, its not uncommon (especially in men it seems) to want to push the boundaries and see how much you can take, that sensation you get when stretched is giddying.....