I am looking for some personal experiences of any lefties out there with fountain pens. I currently own a Pelikano Junior left hander. I was also looking at the petit1 and preppy. I am aware that the more expensive pens have interchangeable nibs, but before I move into that category I was looking for more information on some of these entry level products.

I'm a lefty and have used and collected fountain pens for a long time. I've found that a med. nib is the smoothest. When you get a new pen the nib will get broken in from your writing over time. I'm not real fond of a fine nib - they are just too scratchy. There just isn't enough nib on the paper to glide smoothly on the paper. I only have one "lefty" nib and don't find that it writes any better than a non-lefty nib.

I like both the preppy and the petit 1. I think it depends on your hand position and how you hold your pen that will affect your writing experience.

I think both these pens write with a similar line, about 0.7mm and the nibs are quite smooth. I would say the Petit 1 nib is a bit smoother than the Preppy. The Platinum ink that comes with the Preppy is more accepting to a variety of paper surfaces, where the Pilot ink with the Petit 1 tends to feather and bleed a lot of cheaper papers.

The Preppy can be converted to an eyedropper pen as well, which is a fun option. The only drawback is sometimes it seems the plastic is prone to cracking. I have one barrel that got a slight crack, but I was able to fix it with scotch tape. I have heard others had similar experiences.

The Petit 1 nib is similar to the Varsity V Pen. It has the same nib and construction. Its a short pen, and I like the size of it, but some might find it too small when unposted. Also I have read reviews where people didn't find it as comfortable to write with.

Overall I like both, but maybe you might want to try the Preppy first. It's slightly less expensive, and you won't feel too bad if you try it and it doesn't work out as well as you hope.
Here is a review that might be helpful!:
http://blog.shopwritersbloc.com/fountain_pens/lefthanded_fountain_pen_use_pa.html

I hope you find something that works well for you! :)