Pulmonary/CC is not a very competitive field to get except at top programs like Denver, Univ. of Washington, Penn. To that extent, going to a decent IM program with good exposure to Pulmonary attendings is key in order to get letters. The big lure of Pulmonary right now is the fact that in the "real world" any patient put on a ventilator gets a pulmonary consult. Critical Care keeps you up at night -- something to think about as well.
The most competitive fields to get into out of IM are GI and Cards. I would argue that GI has become the most competitive field to get into out of IM, followed closely by Cards and Allergy. Why? There are only 200-250 GI spots nationwide, compared with 750-800 in Cards. This year, we had 10 people applying for GI spots nationwide, and 12 applying to Cards. So do the math across the country. Many people who thought they were doing Cards have switched to GI. GI procedures still pay pretty well, can be done in more volume since they're not sterile (except for complicated EUS/ERCP cases which are obviously not sterile but are time consuming), and GI affords a much better lifestyle than Cards (yes you get called in at night for bleeders sometimes or stones, but you don't maintain a large inpatient service, which as we all know is extremely time consuming and resource sapping).
With these competitive fields, getting into as strong as an IM program as you can get into is key. PDs and faculty know each other and talk to each other, so going somewhere you can get to know faculty and maybe do some research to get good letters is pretty key. In addition, your best chance of matching in fellowship is where you are in residency (or your own med school, but as you're from India, that's not an issue). So a balance between all these factors is optimal.
If you want to do interventional Cards, there are some things to think about. General Cards fellowships are 3-4 years after IM. Most programs allow those interested in EP to fold in their first year of EP into their last year of general Cards fellowship. None I've heard of allow anyone doing Intervention to do that. Also, many Interventional fellowships are now 2 years rather than 1 (after general Cards) because many fellowships are teaching peripheral vascular techniques as well. Basically, it's a way for programs to get another year out of you. You might say "screw peripheral intervention, I only want to do coronaries" but if you go into private practice, you won't be very marketable unless you know those peripheral skills. Remember that as an interventional Cardiologist you will be on call pretty frequently depending on the group you join, and most average size groups only have 2 or 3 interventionalists in their group -- so you do the math. Also, reimbursement for interventional procedures, like PTCA, have plummeted. One Cardiologist I spoke with said that 2-3 yrs ago he could bill $2-3000 for a 2v PTCA c stenting. In 2002, he said it's now $700-800. All your other costs of practice have stayed the same or gone up, but what you're getting paid has dropped pretty substantially. Bottom line, Interventional Cards (can be as long as 9 years in the worst case scenario, best case 7-8 years) is a pretty substantial time committment, so be prepared for this.
But do what you like first -- whether its scoping or putting a wire in the bile duct, putting a wire down a coronary, or bronching someone.