Forget all this sh!tload of crap you are being told by proponents of "public-says-best" theory.
It ALL depends on which stream you are currently doing, and also on which state you are from and finally on your own skills which syllabus you do.
ICSE needs hardworking dedicated and also intelligent students, and you often end up getting 5% or 10% less than CBSE students in 10th, while students from stupid boards like Karnataka State Board get 10%-15% more than you because they study next to nothing in karnataka.
I took CBSE, but I advice you to go for ICSE from 1st upto 10th whether or not you are good or bad because the learning experience there makes you stronger for 11th and 12th. But going half way through CBSE to ICSE is stupidly dangerous unless you are a really hard worker. This advice is applicable ONLY to those who want to feel how hard work looks like.
Else, join an easy board if you want to just pass 10th and concentrate on future more. You can take up extra-curricular classes upto 10th, while science and commerce students of 11th/12th don't have time for ANYTHING during the mad rat-race for IIT and CA respectively. Its stressful, but FUN when you are about to write the exams. Anyway, trying to manage extracurricular stuff in 10th is good for you because you would be juggling between several coaching classes and school in 12th and this sort of helps you get started and at the same time not loose out on childhood fun.
Anyway, 10th marks don't matter much. Even if you get marks as low as 80% you qualify to great 11th and 12th schools. Instead of wasting your time studying subjects you won't pursue after 10th, I advice you to get your basics strong in those subjects which you intend to pursue in 12th. For example, wannabe PCMC students can forgo parts of Biology in 10th to study physics and mathematics in-depth in 10th to have an easier time in 11th and 12th for example. Same advice applicable for Social for PCMB/PCMC students.
I don't mean forgo as in "don't study" but as in don't push yourself too hard to study them if in the same time you can study much more of another subject.
As far as CBSE is concerned, upto 10th you can manage with Last Minute preparation. DONT DO THAT. I learnt it the hard way. Because in 11th and 12th you need continuous studies for which you need practice right from 10th. Ofcource you will end up completing the syllabus pretty fast that way, but then you can use the extra time to study for future classes, by going to advanced portions of other subjects - I personally recommend you learn Logarithms and Calculus in class 9-10 itself if you have the time - log in 9th and calc in 10th. Because CBSE has a totally messed up 11th and 12th syllabus, which has NO logarithms and at the same time, you USE calculus in chemistry and physics a LOT before even learning them in mathematics which completely screwed my 11th life (you learn calculus only in 12th but use it in 11th).
Funnily enough, when learnt at a young age, Calculus and Logarithms appear damn easy, as I noticed with a friend. You just need a good teacher for that.
And yeah, for an easy and comfortable 11th/12th, you can go from ICSE 10th to State Board 11th/12th if your state's board is riddiculously easy like in Karnataka. Do this if you are going for a Bacholars Course like B.Com whose entrance is based ONLY on marks obtained in 12th exams.